Refactor error handling for SendError struct

Reformat the construction of SendError objects for better readability. This improves the clarity and maintainability of the error handling code within the client.go file.

client.go

@@ -798,13 +798,17 @@ func (c *Client) sendSingleMsg(message *Msg) error {
 	}
 	from, err := message.GetSender(false)
 	if err != nil {
-		return &SendError{Reason: ErrGetSender, errlist: []error{err}, isTemp: isTempError(err),
+		return &SendError{
-			affectedMsg: message}
+			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),
+		return &SendError{
-			affectedMsg: message}
+			Reason: ErrGetRcpts, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
 	}
 
 	if c.dsn {
@@ -813,8 +817,10 @@ func (c *Client) sendSingleMsg(message *Msg) error {
 		}
 	}
 	if err = c.smtpClient.Mail(from); err != nil {
-		retError := &SendError{Reason: ErrSMTPMailFrom, errlist: []error{err}, isTemp: isTempError(err),
+		retError := &SendError{
-			affectedMsg: message}
+			Reason: ErrSMTPMailFrom, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
 		if resetSendErr := c.smtpClient.Reset(); resetSendErr != nil {
 			retError.errlist = append(retError.errlist, resetSendErr)
 		}
@@ -843,28 +849,38 @@ func (c *Client) sendSingleMsg(message *Msg) error {
 	}
 	writer, err := c.smtpClient.Data()
 	if err != nil {
-		return &SendError{Reason: ErrSMTPData, errlist: []error{err}, isTemp: isTempError(err),
+		return &SendError{
-			affectedMsg: message}
+			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),
+		return &SendError{
-			affectedMsg: message}
+			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),
+		return &SendError{
-			affectedMsg: message}
+			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),
+		return &SendError{
-			affectedMsg: message}
+			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),
+		return &SendError{
-			affectedMsg: message}
+			Reason: ErrConnCheck, errlist: []error{err}, isTemp: isTempError(err),
+			affectedMsg: message,
+		}
 	}
 	return nil
 }

senderror_test.go

@@ -83,6 +83,13 @@ 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")
+	}
+}
+
 // 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}