Merge 4b60557518 into 65a91a2711

go-mail goroutine-/thread-safety

.github/workflows/codecov.yml

@@ -36,10 +36,10 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        go: ['1.20', '1.21', '1.22', '1.23']
+        go: ['1.19', '1.20', '1.23']
     steps:
     - name: Harden Runner
-      uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
+      uses: step-security/harden-runner@91182cccc01eb5e619899d80e4e971d6181294a7 # v2.10.1
       with:
         egress-policy: audit
 

.github/workflows/codeql-analysis.yml

@@ -45,7 +45,7 @@ jobs:
 
     steps:
     - name: Harden Runner
-      uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
+      uses: step-security/harden-runner@91182cccc01eb5e619899d80e4e971d6181294a7 # v2.10.1
       with:
         egress-policy: audit
 
@@ -54,7 +54,7 @@ jobs:
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@4dd16135b69a43b6c8efb853346f8437d92d3c93 # v3.26.6
+      uses: github/codeql-action/init@461ef6c76dfe95d5c364de2f431ddbd31a417628 # v3.26.9
       with:
         languages: ${{ matrix.language }}
         # If you wish to specify custom queries, you can do so here or in a config file.
@@ -65,7 +65,7 @@ jobs:
     # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
     # If this step fails, then you should remove it and run the build manually (see below)
     - name: Autobuild
-      uses: github/codeql-action/autobuild@4dd16135b69a43b6c8efb853346f8437d92d3c93 # v3.26.6
+      uses: github/codeql-action/autobuild@461ef6c76dfe95d5c364de2f431ddbd31a417628 # v3.26.9
 
     # ℹ️ Command-line programs to run using the OS shell.
     # 📚 https://git.io/JvXDl
@@ -79,4 +79,4 @@ jobs:
     #   make release
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@4dd16135b69a43b6c8efb853346f8437d92d3c93 # v3.26.6
+      uses: github/codeql-action/analyze@461ef6c76dfe95d5c364de2f431ddbd31a417628 # v3.26.9

.github/workflows/dependency-review.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
+        uses: step-security/harden-runner@91182cccc01eb5e619899d80e4e971d6181294a7 # v2.10.1
         with:
           egress-policy: audit
 

.github/workflows/golangci-lint.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
+        uses: step-security/harden-runner@91182cccc01eb5e619899d80e4e971d6181294a7 # v2.10.1
         with:
           egress-policy: audit
 

.github/workflows/govulncheck.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps: 
     - name: Harden Runner
-      uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
+      uses: step-security/harden-runner@91182cccc01eb5e619899d80e4e971d6181294a7 # v2.10.1
       with:
         egress-policy: audit
     - name: Run govulncheck

.github/workflows/reuse.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps: 
     - name: Harden Runner
-      uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
+      uses: step-security/harden-runner@91182cccc01eb5e619899d80e4e971d6181294a7 # v2.10.1
       with:
         egress-policy: audit
 

.github/workflows/scorecards.yml

@@ -35,7 +35,7 @@ jobs:
 
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
+        uses: step-security/harden-runner@91182cccc01eb5e619899d80e4e971d6181294a7 # v2.10.1
         with:
           egress-policy: audit
 
@@ -75,6 +75,6 @@ jobs:
 
       # Upload the results to GitHub's code scanning dashboard.
       - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@4dd16135b69a43b6c8efb853346f8437d92d3c93 # v3.26.6
+        uses: github/codeql-action/upload-sarif@461ef6c76dfe95d5c364de2f431ddbd31a417628 # v3.26.9
         with:
           sarif_file: results.sarif

.github/workflows/sonarqube.yml

@@ -27,7 +27,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
-        uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
+        uses: step-security/harden-runner@91182cccc01eb5e619899d80e4e971d6181294a7 # v2.10.1
         with:
           egress-policy: audit
 
@@ -44,7 +44,7 @@ jobs:
         run: |
           go test -v -race --coverprofile=./cov.out ./...
 
-      - uses: sonarsource/sonarqube-scan-action@0c0f3958d90fc466625f1d1af1f47bddd4cc6bd1 # master
+      - uses: sonarsource/sonarqube-scan-action@884b79409bbd464b2a59edc326a4b77dc56b2195 # master
         env:
           SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
           SONAR_HOST_URL: ${{ secrets.SONAR_HOST_URL }}

client.go

@@ -12,6 +12,7 @@ import (
 	"net"
 	"os"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/wneessen/go-mail/log"
@@ -87,12 +88,12 @@ type DialContextFunc func(ctx context.Context, network, address string) (net.Con
 
 // Client is the SMTP client struct
 type Client struct {
-	// connection is the net.Conn that the smtp.Client is based on
-	connection net.Conn
-
 	// Timeout for the SMTP server connection
 	connTimeout time.Duration
 
+	// dialContextFunc is a custom DialContext function to dial target SMTP server
+	dialContextFunc DialContextFunc
+
 	// dsn indicates that we want to use DSN for the Client
 	dsn bool
 
@@ -102,11 +103,9 @@ type Client struct {
 	// dsnrntype defines the DSNRcptNotifyOption in case DSN is enabled
 	dsnrntype []string
 
-	// isEncrypted indicates if a Client connection is encrypted or not
+	// fallbackPort is used as an alternative port number in case the primary port is unavailable or
-	isEncrypted bool
+	// fails to bind.
-
+	fallbackPort int
-	// noNoop indicates the Noop is to be skipped
-	noNoop bool
 
 	// HELO/EHLO string for the greeting the target SMTP server
 	helo string
@@ -114,12 +113,24 @@ type Client struct {
 	// Hostname of the target SMTP server to connect to
 	host string
 
+	// isEncrypted indicates if a Client connection is encrypted or not
+	isEncrypted bool
+
+	// logger is a logger that implements the log.Logger interface
+	logger log.Logger
+
+	// mutex is used to synchronize access to shared resources, ensuring that only one goroutine can
+	// modify them at a time.
+	mutex sync.RWMutex
+
+	// noNoop indicates the Noop is to be skipped
+	noNoop bool
+
 	// pass is the corresponding SMTP AUTH password
 	pass string
 
-	// Port of the SMTP server to connect to
+	// port specifies the network port number on which the server listens for incoming connections.
 	port int
-	fallbackPort int
 
 	// smtpAuth is a pointer to smtp.Auth
 	smtpAuth smtp.Auth
@@ -130,26 +141,20 @@ type Client struct {
 	// smtpClient is the smtp.Client that is set up when using the Dial*() methods
 	smtpClient *smtp.Client
 
-	// Use SSL for the connection
-	useSSL bool
-
 	// tlspolicy sets the client to use the provided TLSPolicy for the STARTTLS protocol
 	tlspolicy TLSPolicy
 
 	// tlsconfig represents the tls.Config setting for the STARTTLS connection
 	tlsconfig *tls.Config
 
-	// user is the SMTP AUTH username
-	user string
-
 	// useDebugLog enables the debug logging on the SMTP client
 	useDebugLog bool
 
-	// logger is a logger that implements the log.Logger interface
+	// user is the SMTP AUTH username
-	logger log.Logger
+	user string
 
-	// dialContextFunc is a custom DialContext function to dial target SMTP server
+	// Use SSL for the connection
-	dialContextFunc DialContextFunc
+	useSSL bool
 }
 
 // Option returns a function that can be used for grouping Client options
@@ -550,6 +555,9 @@ func (c *Client) SetLogger(logger log.Logger) {
 
 // SetTLSConfig overrides the current *tls.Config with the given *tls.Config value
 func (c *Client) SetTLSConfig(tlsconfig *tls.Config) error {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
 	if tlsconfig == nil {
 		return ErrInvalidTLSConfig
 	}
@@ -589,6 +597,9 @@ func (c *Client) setDefaultHelo() error {
 
 // DialWithContext establishes a connection to the SMTP server with a given context.Context
 func (c *Client) DialWithContext(dialCtx context.Context) error {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
 	ctx, cancel := context.WithDeadline(dialCtx, time.Now().Add(c.connTimeout))
 	defer cancel()
 
@@ -602,17 +613,16 @@ func (c *Client) DialWithContext(dialCtx context.Context) error {
 			c.dialContextFunc = tlsDialer.DialContext
 		}
 	}
-	var err error
+	connection, err := c.dialContextFunc(ctx, "tcp", c.ServerAddr())
-	c.connection, err = c.dialContextFunc(ctx, "tcp", c.ServerAddr())
 	if err != nil && c.fallbackPort != 0 {
 		// TODO: should we somehow log or append the previous error?
-		c.connection, err = c.dialContextFunc(ctx, "tcp", c.serverFallbackAddr())
+		connection, err = c.dialContextFunc(ctx, "tcp", c.serverFallbackAddr())
 	}
 	if err != nil {
 		return err
 	}
 
-	client, err := smtp.NewClient(c.connection, c.host)
+	client, err := smtp.NewClient(connection, c.host)
 	if err != nil {
 		return err
 	}
@@ -691,7 +701,7 @@ func (c *Client) DialAndSendWithContext(ctx context.Context, messages ...*Msg) e
 // checkConn makes sure that a required server connection is available and extends the
 // connection deadline
 func (c *Client) checkConn() error {
-	if c.connection == nil {
+	if !c.smtpClient.HasConnection() {
 		return ErrNoActiveConnection
 	}
 
@@ -701,7 +711,7 @@ func (c *Client) checkConn() error {
 		}
 	}
 
-	if err := c.connection.SetDeadline(time.Now().Add(c.connTimeout)); err != nil {
+	if err := c.smtpClient.UpdateDeadline(c.connTimeout); err != nil {
 		return ErrDeadlineExtendFailed
 	}
 	return nil
@@ -715,7 +725,7 @@ func (c *Client) serverFallbackAddr() string {
 
 // tls tries to make sure that the STARTTLS requirements are satisfied
 func (c *Client) tls() error {
-	if c.connection == nil {
+	if !c.smtpClient.HasConnection() {
 		return ErrNoActiveConnection
 	}
 	if !c.useSSL && c.tlspolicy != NoTLS {
@@ -787,3 +797,103 @@ func (c *Client) auth() error {
 	}
 	return nil
 }
+
+// sendSingleMsg sends out a single message and returns an error if the transmission/delivery fails.
+// It is invoked by the public Send methods
+func (c *Client) sendSingleMsg(message *Msg) error {
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+
+	if message.encoding == NoEncoding {
+		if ok, _ := c.smtpClient.Extension("8BITMIME"); !ok {
+			return &SendError{Reason: ErrNoUnencoded, isTemp: false, affectedMsg: message}
+		}
+	}
+	from, err := message.GetSender(false)
+	if err != nil {
+		return &SendError{
+			Reason: ErrGetSender, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
+	}
+	rcpts, err := message.GetRecipients()
+	if err != nil {
+		return &SendError{
+			Reason: ErrGetRcpts, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
+	}
+
+	if c.dsn {
+		if c.dsnmrtype != "" {
+			c.smtpClient.SetDSNMailReturnOption(string(c.dsnmrtype))
+		}
+	}
+	if err = c.smtpClient.Mail(from); err != nil {
+		retError := &SendError{
+			Reason: ErrSMTPMailFrom, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
+		if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
+			retError.errlist = append(retError.errlist, resetSendErr)
+		}
+		return retError
+	}
+	hasError := false
+	rcptSendErr := &SendError{affectedMsg: message}
+	rcptSendErr.errlist = make([]error, 0)
+	rcptSendErr.rcpt = make([]string, 0)
+	rcptNotifyOpt := strings.Join(c.dsnrntype, ",")
+	c.smtpClient.SetDSNRcptNotifyOption(rcptNotifyOpt)
+	for _, rcpt := range rcpts {
+		if err = c.smtpClient.Rcpt(rcpt); err != nil {
+			rcptSendErr.Reason = ErrSMTPRcptTo
+			rcptSendErr.errlist = append(rcptSendErr.errlist, err)
+			rcptSendErr.rcpt = append(rcptSendErr.rcpt, rcpt)
+			rcptSendErr.isTemp = isTempError(err)
+			hasError = true
+		}
+	}
+	if hasError {
+		if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
+			rcptSendErr.errlist = append(rcptSendErr.errlist, resetSendErr)
+		}
+		return rcptSendErr
+	}
+	writer, err := c.smtpClient.Data()
+	if err != nil {
+		return &SendError{
+			Reason: ErrSMTPData, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
+	}
+	_, err = message.WriteTo(writer)
+	if err != nil {
+		return &SendError{
+			Reason: ErrWriteContent, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
+	}
+	message.isDelivered = true
+
+	if err = writer.Close(); err != nil {
+		return &SendError{
+			Reason: ErrSMTPDataClose, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
+	}
+
+	if err = c.Reset(); err != nil {
+		return &SendError{
+			Reason: ErrSMTPReset, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
+	}
+	if err = c.checkConn(); err != nil {
+		return &SendError{
+			Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
+	}
+	return nil
+}

client_119.go

@@ -7,111 +7,23 @@
 
 package mail
 
-import "strings"
+import "errors"
 
 // Send sends out the mail message
 func (c *Client) Send(messages ...*Msg) error {
-	if cerr := c.checkConn(); cerr != nil {
+	if err := c.checkConn(); err != nil {
-		return &SendError{Reason: ErrConnCheck, errlist: []error{cerr}, isTemp: isTempError(cerr)}
+		return &SendError{Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err)}
 	}
 	var errs []*SendError
-	for _, message := range messages {
+	for id, message := range messages {
-		message.sendError = nil
+		if sendErr := c.sendSingleMsg(message); sendErr != nil {
-		if message.encoding == NoEncoding {
+			messages[id].sendError = sendErr
-			if ok, _ := c.smtpClient.Extension("8BITMIME"); !ok {
-				sendErr := &SendError{Reason: ErrNoUnencoded, isTemp: false}
-				message.sendError = sendErr
-				errs = append(errs, sendErr)
-				continue
-			}
-		}
-		from, err := message.GetSender(false)
-		if err != nil {
-			sendErr := &SendError{Reason: ErrGetSender, errlist: []error{err}, isTemp: isTempError(err)}
-			message.sendError = sendErr
-			errs = append(errs, sendErr)
-			continue
-		}
-		rcpts, err := message.GetRecipients()
-		if err != nil {
-			sendErr := &SendError{Reason: ErrGetRcpts, errlist: []error{err}, isTemp: isTempError(err)}
-			message.sendError = sendErr
-			errs = append(errs, sendErr)
-			continue
-		}
 
-		if c.dsn {
+			var msgSendErr *SendError
-			if c.dsnmrtype != "" {
+			if errors.As(sendErr, &msgSendErr) {
-				c.smtpClient.SetDSNMailReturnOption(string(c.dsnmrtype))
+				errs = append(errs, msgSendErr)
 			}
 		}
-		if err = c.smtpClient.Mail(from); err != nil {
-			sendErr := &SendError{Reason: ErrSMTPMailFrom, errlist: []error{err}, isTemp: isTempError(err)}
-			if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
-				sendErr.errlist = append(sendErr.errlist, resetSendErr)
-			}
-			message.sendError = sendErr
-			errs = append(errs, sendErr)
-			continue
-		}
-		failed := false
-		rcptSendErr := &SendError{}
-		rcptSendErr.errlist = make([]error, 0)
-		rcptSendErr.rcpt = make([]string, 0)
-		rcptNotifyOpt := strings.Join(c.dsnrntype, ",")
-		c.smtpClient.SetDSNRcptNotifyOption(rcptNotifyOpt)
-		for _, rcpt := range rcpts {
-			if err = c.smtpClient.Rcpt(rcpt); err != nil {
-				rcptSendErr.Reason = ErrSMTPRcptTo
-				rcptSendErr.errlist = append(rcptSendErr.errlist, err)
-				rcptSendErr.rcpt = append(rcptSendErr.rcpt, rcpt)
-				rcptSendErr.isTemp = isTempError(err)
-				failed = true
-			}
-		}
-		if failed {
-			if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
-				rcptSendErr.errlist = append(rcptSendErr.errlist, err)
-			}
-			message.sendError = rcptSendErr
-			errs = append(errs, rcptSendErr)
-			continue
-		}
-		writer, err := c.smtpClient.Data()
-		if err != nil {
-			sendErr := &SendError{Reason: ErrSMTPData, errlist: []error{err}, isTemp: isTempError(err)}
-			message.sendError = sendErr
-			errs = append(errs, sendErr)
-			continue
-		}
-		_, err = message.WriteTo(writer)
-		if err != nil {
-			sendErr := &SendError{Reason: ErrWriteContent, errlist: []error{err}, isTemp: isTempError(err)}
-			message.sendError = sendErr
-			errs = append(errs, sendErr)
-			continue
-		}
-		message.isDelivered = true
-
-		if err = writer.Close(); err != nil {
-			sendErr := &SendError{Reason: ErrSMTPDataClose, errlist: []error{err}, isTemp: isTempError(err)}
-			message.sendError = sendErr
-			errs = append(errs, sendErr)
-			continue
-		}
-
-		if err = c.Reset(); err != nil {
-			sendErr := &SendError{Reason: ErrSMTPReset, errlist: []error{err}, isTemp: isTempError(err)}
-			message.sendError = sendErr
-			errs = append(errs, sendErr)
-			continue
-		}
-		if err = c.checkConn(); err != nil {
-			sendErr := &SendError{Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err)}
-			message.sendError = sendErr
-			errs = append(errs, sendErr)
-			continue
-		}
 	}
 
 	if len(errs) > 0 {

client_120.go

@@ -9,7 +9,6 @@ package mail
 
 import (
 	"errors"
-	"strings"
 )
 
 // Send sends out the mail message
@@ -18,92 +17,16 @@ func (c *Client) Send(messages ...*Msg) (returnErr error) {
 		returnErr = &SendError{Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err)}
 		return
 	}
-	for _, message := range messages {
-		message.sendError = nil
-		if message.encoding == NoEncoding {
-			if ok, _ := c.smtpClient.Extension("8BITMIME"); !ok {
-				message.sendError = &SendError{Reason: ErrNoUnencoded, isTemp: false}
-				returnErr = errors.Join(returnErr, message.sendError)
-				continue
-			}
-		}
-		from, err := message.GetSender(false)
-		if err != nil {
-			message.sendError = &SendError{Reason: ErrGetSender, errlist: []error{err}, isTemp: isTempError(err)}
-			returnErr = errors.Join(returnErr, message.sendError)
-			continue
-		}
-		rcpts, err := message.GetRecipients()
-		if err != nil {
-			message.sendError = &SendError{Reason: ErrGetRcpts, errlist: []error{err}, isTemp: isTempError(err)}
-			returnErr = errors.Join(returnErr, message.sendError)
-			continue
-		}
 
-		if c.dsn {
+	var errs []error
-			if c.dsnmrtype != "" {
+	defer func() {
-				c.smtpClient.SetDSNMailReturnOption(string(c.dsnmrtype))
+		returnErr = errors.Join(errs...)
-			}
+	}()
-		}
-		if err = c.smtpClient.Mail(from); err != nil {
-			message.sendError = &SendError{Reason: ErrSMTPMailFrom, errlist: []error{err}, isTemp: isTempError(err)}
-			returnErr = errors.Join(returnErr, message.sendError)
-			if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
-				returnErr = errors.Join(returnErr, resetSendErr)
-			}
-			continue
-		}
-		failed := false
-		rcptSendErr := &SendError{}
-		rcptSendErr.errlist = make([]error, 0)
-		rcptSendErr.rcpt = make([]string, 0)
-		rcptNotifyOpt := strings.Join(c.dsnrntype, ",")
-		c.smtpClient.SetDSNRcptNotifyOption(rcptNotifyOpt)
-		for _, rcpt := range rcpts {
-			if err = c.smtpClient.Rcpt(rcpt); err != nil {
-				rcptSendErr.Reason = ErrSMTPRcptTo
-				rcptSendErr.errlist = append(rcptSendErr.errlist, err)
-				rcptSendErr.rcpt = append(rcptSendErr.rcpt, rcpt)
-				rcptSendErr.isTemp = isTempError(err)
-				failed = true
-			}
-		}
-		if failed {
-			if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
-				returnErr = errors.Join(returnErr, resetSendErr)
-			}
-			message.sendError = rcptSendErr
-			returnErr = errors.Join(returnErr, message.sendError)
-			continue
-		}
-		writer, err := c.smtpClient.Data()
-		if err != nil {
-			message.sendError = &SendError{Reason: ErrSMTPData, errlist: []error{err}, isTemp: isTempError(err)}
-			returnErr = errors.Join(returnErr, message.sendError)
-			continue
-		}
-		_, err = message.WriteTo(writer)
-		if err != nil {
-			message.sendError = &SendError{Reason: ErrWriteContent, errlist: []error{err}, isTemp: isTempError(err)}
-			returnErr = errors.Join(returnErr, message.sendError)
-			continue
-		}
-		message.isDelivered = true
 
-		if err = writer.Close(); err != nil {
+	for id, message := range messages {
-			message.sendError = &SendError{Reason: ErrSMTPDataClose, errlist: []error{err}, isTemp: isTempError(err)}
+		if sendErr := c.sendSingleMsg(message); sendErr != nil {
-			returnErr = errors.Join(returnErr, message.sendError)
+			messages[id].sendError = sendErr
-			continue
+			errs = append(errs, sendErr)
-		}
-
-		if err = c.Reset(); err != nil {
-			message.sendError = &SendError{Reason: ErrSMTPReset, errlist: []error{err}, isTemp: isTempError(err)}
-			returnErr = errors.Join(returnErr, message.sendError)
-			continue
-		}
-		if err = c.checkConn(); err != nil {
-			message.sendError = &SendError{Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err)}
-			returnErr = errors.Join(returnErr, message.sendError)
 		}
 	}
 

msg.go

@@ -481,8 +481,8 @@ func (m *Msg) SetMessageID() {
 	if err != nil {
 		hostname = "localhost.localdomain"
 	}
-	randNumPrimary, _ := randNum(100000000)
+	randNumPrimary := randNum(100000000)
-	randNumSecondary, _ := randNum(10000)
+	randNumSecondary := randNum(10000)
 	randString, _ := randomStringSecure(17)
 	procID := os.Getpid() * randNumSecondary
 	messageID := fmt.Sprintf("%d.%d%d.%s@%s", procID, randNumPrimary, randNumSecondary,
@@ -490,6 +490,17 @@ func (m *Msg) SetMessageID() {
 	m.SetMessageIDWithValue(messageID)
 }
 
+// GetMessageID returns the message ID of the Msg as string value. If no message ID
+// is set, an empty string will be returned
+func (m *Msg) GetMessageID() string {
+	if msgidheader, ok := m.genHeader[HeaderMessageID]; ok {
+		if len(msgidheader) > 0 {
+			return msgidheader[0]
+		}
+	}
+	return ""
+}
+
 // SetMessageIDWithValue sets the message id for the mail
 func (m *Msg) SetMessageIDWithValue(messageID string) {
 	m.SetGenHeader(HeaderMessageID, fmt.Sprintf("<%s>", messageID))

msg_nowin_test.go

@@ -61,3 +61,25 @@ func TestMsg_WriteToSendmail(t *testing.T) {
 		t.Errorf("WriteToSendmail failed: %s", err)
 	}
 }
+
+func TestMsg_WriteToTempFileFailed(t *testing.T) {
+	m := NewMsg()
+	_ = m.From("Toni Tester <tester@example.com>")
+	_ = m.To("Ellenor Tester <ellinor@example.com>")
+	m.SetBodyString(TypeTextPlain, "This is a test")
+
+	curTmpDir := os.Getenv("TMPDIR")
+	defer func() {
+		if err := os.Setenv("TMPDIR", curTmpDir); err != nil {
+			t.Errorf("failed to set TMPDIR environment variable: %s", err)
+		}
+	}()
+
+	if err := os.Setenv("TMPDIR", "/invalid/directory/that/does/not/exist"); err != nil {
+		t.Errorf("failed to set TMPDIR environment variable: %s", err)
+	}
+	_, err := m.WriteToTempFile()
+	if err == nil {
+		t.Errorf("WriteToTempFile() did not fail as expected")
+	}
+}

msg_test.go

@@ -786,13 +786,11 @@ func TestMsg_SetMessageIDWithValue(t *testing.T) {
 // TestMsg_SetMessageIDRandomness tests the randomness of Msg.SetMessageID methods
 func TestMsg_SetMessageIDRandomness(t *testing.T) {
 	var mids []string
-	for i := 0; i < 100; i++ {
+	for i := 0; i < 50_000; i++ {
 		m := NewMsg()
 		m.SetMessageID()
-		mid := m.GetGenHeader(HeaderMessageID)
+		mid := m.GetMessageID()
-		if len(mid) > 0 {
+		mids = append(mids, mid)
-			mids = append(mids, mid[0])
-		}
 	}
 	c := make(map[string]int)
 	for i := range mids {
@@ -805,6 +803,21 @@ func TestMsg_SetMessageIDRandomness(t *testing.T) {
 	}
 }
 
+func TestMsg_GetMessageID(t *testing.T) {
+	expected := "this.is.a.message.id"
+	msg := NewMsg()
+	msg.SetMessageIDWithValue(expected)
+	val := msg.GetMessageID()
+	if !strings.EqualFold(val, fmt.Sprintf("<%s>", expected)) {
+		t.Errorf("GetMessageID() failed. Expected: %s, got: %s", fmt.Sprintf("<%s>", expected), val)
+	}
+	msg.genHeader[HeaderMessageID] = nil
+	val = msg.GetMessageID()
+	if val != "" {
+		t.Errorf("GetMessageID() failed. Expected empty string, got: %s", val)
+	}
+}
+
 // TestMsg_FromFormat tests the FromFormat and EnvelopeFrom methods for the Msg object
 func TestMsg_FromFormat(t *testing.T) {
 	tests := []struct {

random.go

@@ -7,8 +7,6 @@ package mail
 import (
 	"crypto/rand"
 	"encoding/binary"
-	"fmt"
-	"math/big"
 	"strings"
 )
 
@@ -52,23 +50,3 @@ func randomStringSecure(length int) (string, error) {
 
 	return randString.String(), nil
 }
-
-// randNum returns a random number with a maximum value of length
-func randNum(length int) (int, error) {
-	if length <= 0 {
-		return 0, fmt.Errorf("provided number is <= 0: %d", length)
-	}
-	length64 := big.NewInt(int64(length))
-	if !length64.IsUint64() {
-		return 0, fmt.Errorf("big.NewInt() generation returned negative value: %d", length64)
-	}
-	randNum64, err := rand.Int(rand.Reader, length64)
-	if err != nil {
-		return 0, err
-	}
-	randomNum := int(randNum64.Int64())
-	if randomNum < 0 {
-		return 0, fmt.Errorf("generated random number does not fit as int64: %d", randNum64)
-	}
-	return randomNum, nil
-}

random_119.go

@@ -0,0 +1,22 @@
+// SPDX-FileCopyrightText: 2022-2023 The go-mail Authors
+//
+// SPDX-License-Identifier: MIT
+
+//go:build !go1.20
+// +build !go1.20
+
+package mail
+
+import (
+	"math/rand"
+	"time"
+)
+
+// randNum returns a random number with a maximum value of length
+func randNum(maxval int) int {
+	if maxval <= 0 {
+		return 0
+	}
+	rand.Seed(time.Now().UnixNano())
+	return rand.Intn(maxval)
+}

random_121.go

@@ -0,0 +1,20 @@
+// SPDX-FileCopyrightText: 2022-2023 The go-mail Authors
+//
+// SPDX-License-Identifier: MIT
+
+//go:build go1.20 && !go1.22
+// +build go1.20,!go1.22
+
+package mail
+
+import (
+	"math/rand"
+)
+
+// randNum returns a random number with a maximum value of length
+func randNum(maxval int) int {
+	if maxval <= 0 {
+		return 0
+	}
+	return rand.Intn(maxval)
+}

random_122.go

@@ -0,0 +1,22 @@
+// SPDX-FileCopyrightText: 2022-2023 The go-mail Authors
+//
+// SPDX-License-Identifier: MIT
+
+//go:build go1.22
+// +build go1.22
+
+package mail
+
+import (
+	"math/rand/v2"
+)
+
+// randNum returns a random number with a maximum value of maxval.
+// go-mail compiled with Go 1.22+ will make use of the novel math/rand/v2 interface
+// Older versions of Go will use math/rand
+func randNum(maxval int) int {
+	if maxval <= 0 {
+		return 0
+	}
+	return rand.IntN(maxval)
+}

random_test.go

@@ -55,16 +55,17 @@ func TestRandomNum(t *testing.T) {
 
 	for _, tc := range tt {
 		t.Run(tc.testName, func(t *testing.T) {
-			rn, err := randNum(tc.max)
+			rn := randNum(tc.max)
-			if err != nil {
-				t.Errorf("random number generation failed: %s", err)
-			}
-			if rn < 0 {
-				t.Errorf("random number generation failed: %d is smaller than zero", rn)
-			}
 			if rn > tc.max {
 				t.Errorf("random number generation failed: %d is bigger than given value %d", rn, tc.max)
 			}
 		})
 	}
 }
+
+func TestRandomNumZero(t *testing.T) {
+	rn := randNum(0)
+	if rn != 0 {
+		t.Errorf("random number generation failed: %d is not zero", rn)
+	}
+}

senderror.go

@@ -56,10 +56,11 @@ const (
 
 // SendError is an error wrapper for delivery errors of the Msg
 type SendError struct {
-	Reason  SendErrReason
+	affectedMsg *Msg
-	isTemp  bool
 	errlist     []error
+	isTemp      bool
 	rcpt        []string
+	Reason      SendErrReason
 }
 
 // SendErrReason represents a comparable reason on why the delivery failed
@@ -92,6 +93,11 @@ func (e *SendError) Error() string {
 			}
 		}
 	}
+	if e.affectedMsg != nil && e.affectedMsg.GetMessageID() != "" {
+		errMessage.WriteString(", affected message ID: ")
+		errMessage.WriteString(e.affectedMsg.GetMessageID())
+	}
+
 	return errMessage.String()
 }
 
@@ -112,6 +118,23 @@ func (e *SendError) IsTemp() bool {
 	return e.isTemp
 }
 
+// MessageID returns the message ID of the affected Msg that caused the error
+// If no message ID was set for the Msg, an empty string will be returned
+func (e *SendError) MessageID() string {
+	if e == nil || e.affectedMsg == nil {
+		return ""
+	}
+	return e.affectedMsg.GetMessageID()
+}
+
+// Msg returns the pointer to the affected message that caused the error
+func (e *SendError) Msg() *Msg {
+	if e == nil || e.affectedMsg == nil {
+		return nil
+	}
+	return e.affectedMsg
+}
+
 // String implements the Stringer interface for the SendErrReason
 func (r SendErrReason) String() string {
 	switch r {

senderror_test.go

@@ -83,7 +83,96 @@ func TestSendError_IsTemp(t *testing.T) {
 	}
 }
 
+func TestSendError_IsTempNil(t *testing.T) {
+	var se *SendError
+	if se.IsTemp() {
+		t.Error("expected false on nil-senderror")
+	}
+}
+
+func TestSendError_MessageID(t *testing.T) {
+	var se *SendError
+	err := returnSendError(ErrAmbiguous, false)
+	if !errors.As(err, &se) {
+		t.Errorf("error mismatch, expected error to be of type *SendError")
+		return
+	}
+	if errors.As(err, &se) {
+		if se.MessageID() == "" {
+			t.Errorf("sendError expected message-id, but got empty string")
+		}
+		if !strings.EqualFold(se.MessageID(), "<this.is.a.message.id>") {
+			t.Errorf("sendError message-id expected: %s, but got: %s", "<this.is.a.message.id>",
+				se.MessageID())
+		}
+	}
+}
+
+func TestSendError_MessageIDNil(t *testing.T) {
+	var se *SendError
+	if se.MessageID() != "" {
+		t.Error("expected empty string on nil-senderror")
+	}
+}
+
+func TestSendError_Msg(t *testing.T) {
+	var se *SendError
+	err := returnSendError(ErrAmbiguous, false)
+	if !errors.As(err, &se) {
+		t.Errorf("error mismatch, expected error to be of type *SendError")
+		return
+	}
+	if errors.As(err, &se) {
+		if se.Msg() == nil {
+			t.Errorf("sendError expected msg pointer, but got nil")
+		}
+		from := se.Msg().GetFromString()
+		if len(from) == 0 {
+			t.Errorf("sendError expected msg from, but got empty string")
+			return
+		}
+		if !strings.EqualFold(from[0], "<toni.tester@domain.tld>") {
+			t.Errorf("sendError message from expected: %s, but got: %s", "<toni.tester@domain.tld>",
+				from[0])
+		}
+	}
+}
+
+func TestSendError_MsgNil(t *testing.T) {
+	var se *SendError
+	if se.Msg() != nil {
+		t.Error("expected nil on nil-senderror")
+	}
+}
+
+func TestSendError_IsFail(t *testing.T) {
+	err1 := returnSendError(ErrAmbiguous, false)
+	err2 := returnSendError(ErrSMTPMailFrom, false)
+	if errors.Is(err1, err2) {
+		t.Errorf("error mismatch, ErrAmbiguous should not be equal to ErrSMTPMailFrom")
+	}
+}
+
+func TestSendError_ErrorMulti(t *testing.T) {
+	expected := `ambiguous reason, check Msg.SendError for message specific reasons, ` +
+		`affected recipient(s): <email1@domain.tld>, <email2@domain.tld>`
+	err := &SendError{
+		Reason: ErrAmbiguous, isTemp: false, affectedMsg: nil,
+		rcpt: []string{"<email1@domain.tld>", "<email2@domain.tld>"},
+	}
+	if err.Error() != expected {
+		t.Errorf("error mismatch, expected: %s, got: %s", expected, err.Error())
+	}
+}
+
 // returnSendError is a helper method to retunr a SendError with a specific reason
 func returnSendError(r SendErrReason, t bool) error {
-	return &SendError{Reason: r, isTemp: t}
+	message := NewMsg()
+	_ = message.From("toni.tester@domain.tld")
+	_ = message.To("tina.tester@domain.tld")
+	message.Subject("This is the subject")
+	message.SetBodyString(TypeTextPlain, "This is the message body")
+	message.SetMessageIDWithValue("this.is.a.message.id")
+
+	return &SendError{Reason: r, isTemp: t, affectedMsg: message}
 }

smtp/smtp.go

@@ -30,34 +30,57 @@ import (
 	"net/textproto"
 	"os"
 	"strings"
+	"sync"
+	"time"
 
 	"github.com/wneessen/go-mail/log"
 )
 
 // A Client represents a client connection to an SMTP server.
 type Client struct {
-	// Text is the textproto.Conn used by the Client. It is exported to allow for
+	// Text is the textproto.Conn used by the Client. It is exported to allow for clients to add extensions.
-	// clients to add extensions.
 	Text *textproto.Conn
-	// keep a reference to the connection so it can be used to create a TLS
+
-	// connection later
+	// auth supported auth mechanisms
-	conn net.Conn
-	// whether the Client is using TLS
-	tls        bool
-	serverName string
-	// map of supported extensions
-	ext map[string]string
-	// supported auth mechanisms
 	auth []string
+
+	// keep a reference to the connection so it can be used to create a TLS connection later
+	conn net.Conn
+
+	// debug logging is enabled
+	debug bool
+
+	// didHello indicates whether we've said HELO/EHLO
+	didHello bool
+
+	// dsnmrtype defines the mail return option in case DSN is enabled
+	dsnmrtype string
+
+	// dsnrntype defines the recipient notify option in case DSN is enabled
+	dsnrntype string
+
+	// ext is a map of supported extensions
+	ext map[string]string
+
+	// helloError is the error from the hello
+	helloError error
+
+	// localName is the name to use in HELO/EHLO
 	localName string // the name to use in HELO/EHLO
-	didHello   bool   // whether we've said HELO/EHLO
+
-	helloError error  // the error from the hello
+	// logger will be used for debug logging
-	// debug logging
+	logger log.Logger
-	debug  bool       // debug logging is enabled
+
-	logger log.Logger // logger will be used for debug logging
+	// mutex is used to synchronize access to shared resources, ensuring that only one goroutine can access
-	// DSN support
+	// the resource at a time.
-	dsnmrtype string // dsnmrtype defines the mail return option in case DSN is enabled
+	mutex sync.RWMutex
-	dsnrntype string // dsnrntype defines the recipient notify option in case DSN is enabled
+
+	// tls indicates whether the Client is using TLS
+	tls bool
+
+	// serverName denotes the name of the server to which the application will connect. Used for
+	// identification and routing.
+	serverName string
 }
 
 // Dial returns a new [Client] connected to an SMTP server at addr.
@@ -94,7 +117,10 @@ func NewClient(conn net.Conn, host string) (*Client, error) {
 
 // Close closes the connection.
 func (c *Client) Close() error {
-	return c.Text.Close()
+	c.mutex.Lock()
+	err := c.Text.Close()
+	c.mutex.Unlock()
+	return err
 }
 
 // hello runs a hello exchange if needed.
@@ -121,28 +147,39 @@ func (c *Client) Hello(localName string) error {
 	if c.didHello {
 		return errors.New("smtp: Hello called after other methods")
 	}
+
+	c.mutex.Lock()
 	c.localName = localName
+	c.mutex.Unlock()
+
 	return c.hello()
 }
 
 // cmd is a convenience function that sends a command and returns the response
 func (c *Client) cmd(expectCode int, format string, args ...interface{}) (int, string, error) {
+	c.mutex.Lock()
+
 	c.debugLog(log.DirClientToServer, format, args...)
 	id, err := c.Text.Cmd(format, args...)
 	if err != nil {
+		c.mutex.Unlock()
 		return 0, "", err
 	}
 	c.Text.StartResponse(id)
-	defer c.Text.EndResponse(id)
 	code, msg, err := c.Text.ReadResponse(expectCode)
 	c.debugLog(log.DirServerToClient, "%d %s", code, msg)
+	c.Text.EndResponse(id)
+	c.mutex.Unlock()
 	return code, msg, err
 }
 
 // helo sends the HELO greeting to the server. It should be used only when the
 // server does not support ehlo.
 func (c *Client) helo() error {
+	c.mutex.Lock()
 	c.ext = nil
+	c.mutex.Unlock()
+
 	_, _, err := c.cmd(250, "HELO %s", c.localName)
 	return err
 }
@@ -157,9 +194,13 @@ func (c *Client) StartTLS(config *tls.Config) error {
 	if err != nil {
 		return err
 	}
+
+	c.mutex.Lock()
 	c.conn = tls.Client(c.conn, config)
 	c.Text = textproto.NewConn(c.conn)
 	c.tls = true
+	c.mutex.Unlock()
+
 	return c.ehlo()
 }
 
@@ -167,11 +208,15 @@ func (c *Client) StartTLS(config *tls.Config) error {
 // The return values are their zero values if [Client.StartTLS] did
 // not succeed.
 func (c *Client) TLSConnectionState() (state tls.ConnectionState, ok bool) {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+
 	tc, ok := c.conn.(*tls.Conn)
 	if !ok {
 		return
 	}
-	return tc.ConnectionState(), true
+	state, ok = tc.ConnectionState(), true
+	return
 }
 
 // Verify checks the validity of an email address on the server.
@@ -257,6 +302,8 @@ func (c *Client) Mail(from string) error {
 		return err
 	}
 	cmdStr := "MAIL FROM:<%s>"
+
+	c.mutex.RLock()
 	if c.ext != nil {
 		if _, ok := c.ext["8BITMIME"]; ok {
 			cmdStr += " BODY=8BITMIME"
@@ -269,6 +316,8 @@ func (c *Client) Mail(from string) error {
 			cmdStr += fmt.Sprintf(" RET=%s", c.dsnmrtype)
 		}
 	}
+	c.mutex.RUnlock()
+
 	_, _, err := c.cmd(250, cmdStr, from)
 	return err
 }
@@ -280,7 +329,11 @@ func (c *Client) Rcpt(to string) error {
 	if err := validateLine(to); err != nil {
 		return err
 	}
+
+	c.mutex.RLock()
 	_, ok := c.ext["DSN"]
+	c.mutex.RUnlock()
+
 	if ok && c.dsnrntype != "" {
 		_, _, err := c.cmd(25, "RCPT TO:<%s> NOTIFY=%s", to, c.dsnrntype)
 		return err
@@ -294,12 +347,23 @@ type dataCloser struct {
 	io.WriteCloser
 }
 
+// Close releases the lock, closes the WriteCloser, waits for a response, and then returns any error encountered.
 func (d *dataCloser) Close() error {
+	d.c.mutex.Lock()
 	_ = d.WriteCloser.Close()
 	_, _, err := d.c.Text.ReadResponse(250)
+	d.c.mutex.Unlock()
 	return err
 }
 
+// Write writes data to the underlying WriteCloser while ensuring thread-safety by locking and unlocking a mutex.
+func (d *dataCloser) Write(p []byte) (n int, err error) {
+	d.c.mutex.Lock()
+	n, err = d.WriteCloser.Write(p)
+	d.c.mutex.Unlock()
+	return
+}
+
 // Data issues a DATA command to the server and returns a writer that
 // can be used to write the mail headers and body. The caller should
 // close the writer before calling any more methods on c. A call to
@@ -309,7 +373,14 @@ func (c *Client) Data() (io.WriteCloser, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &dataCloser{c, c.Text.DotWriter()}, nil
+	datacloser := &dataCloser{}
+
+	c.mutex.Lock()
+	datacloser.c = c
+	datacloser.WriteCloser = c.Text.DotWriter()
+	c.mutex.Unlock()
+
+	return datacloser, nil
 }
 
 var testHookStartTLS func(*tls.Config) // nil, except for tests
@@ -405,7 +476,10 @@ func (c *Client) Extension(ext string) (bool, string) {
 		return false, ""
 	}
 	ext = strings.ToUpper(ext)
+
+	c.mutex.RLock()
 	param, ok := c.ext[ext]
+	c.mutex.RUnlock()
 	return ok, param
 }
 
@@ -438,7 +512,11 @@ func (c *Client) Quit() error {
 	if err != nil {
 		return err
 	}
-	return c.Text.Close()
+	c.mutex.Lock()
+	err = c.Text.Close()
+	c.mutex.Unlock()
+
+	return err
 }
 
 // SetDebugLog enables the debug logging for incoming and outgoing SMTP messages
@@ -472,6 +550,21 @@ func (c *Client) SetDSNRcptNotifyOption(d string) {
 	c.dsnrntype = d
 }
 
+// HasConnection checks if the client has an active connection.
+// Returns true if the `conn` field is not nil, indicating an active connection.
+func (c *Client) HasConnection() bool {
+	return c.conn != nil
+}
+
+func (c *Client) UpdateDeadline(timeout time.Duration) error {
+	c.mutex.Lock()
+	if err := c.conn.SetDeadline(time.Now().Add(timeout)); err != nil {
+		return fmt.Errorf("smtp: failed to update deadline: %w", err)
+	}
+	c.mutex.Unlock()
+	return nil
+}
+
 // debugLog checks if the debug flag is set and if so logs the provided message to
 // the log.Logger interface
 func (c *Client) debugLog(d log.Direction, f string, a ...interface{}) {

smtp/smtp_ehlo.go

@@ -25,6 +25,9 @@ func (c *Client) ehlo() error {
 	if err != nil {
 		return err
 	}
+
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
 	ext := make(map[string]string)
 	extList := strings.Split(msg, "\n")
 	if len(extList) > 1 {

smtp/smtp_ehlo_117.go

@@ -22,12 +22,15 @@ import "strings"
 // should be the preferred greeting for servers that support it.
 //
 // Backport of: https://github.com/golang/go/commit/4d8db00641cc9ff4f44de7df9b8c4f4a4f9416ee#diff-4f6f6bdb9891d4dd271f9f31430420a2e44018fe4ee539576faf458bebb3cee4
-// to guarantee backwards compatibility with Go 1.16/1.17:w
+// to guarantee backwards compatibility with Go 1.16/1.17
 func (c *Client) ehlo() error {
 	_, msg, err := c.cmd(250, "EHLO %s", c.localName)
 	if err != nil {
 		return err
 	}
+
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
 	ext := make(map[string]string)
 	extList := strings.Split(msg, "\n")
 	if len(extList) > 1 {