Refactor Client struct to improve organization and clarity

Rearranged and grouped struct fields more logically within Client. Introduced the dialContextFunc and fallbackPort fields to enhance connection flexibility. Minor code style adjustments were also made for better readability.

client.go

@@ -88,13 +88,15 @@ type DialContextFunc func(ctx context.Context, network, address string) (net.Con
 
 // Client is the SMTP client struct
 type Client struct {
-	mutex sync.RWMutex
 	// 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
 
@@ -104,11 +106,9 @@ type Client struct {
 	// dsnrntype defines the DSNRcptNotifyOption in case DSN is enabled
 	dsnrntype []string
 
-	// isEncrypted indicates if a Client connection is encrypted or not
-	isEncrypted bool
-
-	// noNoop indicates the Noop is to be skipped
-	noNoop bool
+	// fallbackPort is used as an alternative port number in case the primary port is unavailable or
+	// fails to bind.
+	fallbackPort int
 
 	// HELO/EHLO string for the greeting the target SMTP server
 	helo string
@@ -116,12 +116,24 @@ 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
@@ -132,26 +144,20 @@ 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
-	logger log.Logger
+	// user is the SMTP AUTH username
+	user string
 
-	// dialContextFunc is a custom DialContext function to dial target SMTP server
-	dialContextFunc DialContextFunc
+	// Use SSL for the connection
+	useSSL bool
 }
 
 // Option returns a function that can be used for grouping Client options