Enhance comments with detailed explanations and links

Improved comments for better clarity by detailing the purpose of each constant and type, and included relevant RFC links for deeper context. These changes aim to help developers quickly understand the code without needing to cross-reference external documents.

client.go

@@ -19,67 +19,74 @@ import (
 	"github.com/wneessen/go-mail/smtp"
 )
 
-// Defaults
 const (
-	// DefaultPort is the default connection port to the SMTP server
+	// DefaultPort is the default connection port to the SMTP server.
 	DefaultPort = 25
 
-	// DefaultPortSSL is the default connection port for SSL/TLS to the SMTP server
+	// DefaultPortSSL is the default connection port for SSL/TLS to the SMTP server.
 	DefaultPortSSL = 465
 
-	// DefaultPortTLS is the default connection port for STARTTLS to the SMTP server
+	// DefaultPortTLS is the default connection port for STARTTLS to the SMTP server.
 	DefaultPortTLS = 587
 
-	// DefaultTimeout is the default connection timeout
+	// DefaultTimeout is the default connection timeout.
 	DefaultTimeout = time.Second * 15
 
-	// DefaultTLSPolicy is the default STARTTLS policy
+	// DefaultTLSPolicy specifies the default TLS policy for connections.
 	DefaultTLSPolicy = TLSMandatory
 
-	// DefaultTLSMinVersion is the minimum TLS version required for the connection
-	// Nowadays TLS1.2 should be the sane default
+	// DefaultTLSMinVersion defines the minimum TLS version to be used for secure connections.
+	// Nowadays TLS 1.2 is assumed be a sane default.
 	DefaultTLSMinVersion = tls.VersionTLS12
 )
 
-// DSNMailReturnOption is a type to define which MAIL RET option is used when a DSN
-// is requested
-type DSNMailReturnOption string
+type (
 
-// DSNRcptNotifyOption is a type to define which RCPT NOTIFY option is used when a DSN
-// is requested
-type DSNRcptNotifyOption string
+	// DSNMailReturnOption is a type wrapper for a string and specifies the type of return content requested
+	// in a Delivery Status Notification (DSN).
+	// https://datatracker.ietf.org/doc/html/rfc1891/
+	DSNMailReturnOption string
+
+	// DSNRcptNotifyOption is a type wrapper for a string and specifies the notification options for a
+	// recipient in DSNs.
+	// https://datatracker.ietf.org/doc/html/rfc1891/
+	DSNRcptNotifyOption string
+)
 
 const (
-	// DSNMailReturnHeadersOnly requests that only the headers of the message be returned.
-	// See: https://www.rfc-editor.org/rfc/rfc1891#section-5.3
+
+	// DSNMailReturnHeadersOnly requests that only the message headers of the mail message are returned in
+	// a DSN (Delivery Status Notification).
+	// https://datatracker.ietf.org/doc/html/rfc1891#section-5.3
 	DSNMailReturnHeadersOnly DSNMailReturnOption = "HDRS"
 
-	// DSNMailReturnFull requests that the entire message be returned in any "failed"
-	// delivery status notification issued for this recipient
-	// See: https://www.rfc-editor.org/rfc/rfc1891#section-5.3
+	// DSNMailReturnFull requests that the entire mail message is returned in any failed  DSN
+	// (Delivery Status Notification) issued for this recipient.
+	// https://datatracker.ietf.org/doc/html/rfc1891/#section-5.3
 	DSNMailReturnFull DSNMailReturnOption = "FULL"
 
-	// DSNRcptNotifyNever requests that a DSN not be returned to the sender under
-	// any conditions.
-	// See: https://www.rfc-editor.org/rfc/rfc1891#section-5.1
+	// DSNRcptNotifyNever indicates that no DSN (Delivery Status Notifications) should be sent for the
+	// recipient under any condition.
+	// https://datatracker.ietf.org/doc/html/rfc1891/#section-5.1
 	DSNRcptNotifyNever DSNRcptNotifyOption = "NEVER"
 
-	// DSNRcptNotifySuccess requests that a DSN be issued on successful delivery
-	// See: https://www.rfc-editor.org/rfc/rfc1891#section-5.1
+	// DSNRcptNotifySuccess indicates that the sender requests a DSN (Delivery Status Notification) if the
+	// message is successfully delivered.
+	// https://datatracker.ietf.org/doc/html/rfc1891/#section-5.1
 	DSNRcptNotifySuccess DSNRcptNotifyOption = "SUCCESS"
 
-	// DSNRcptNotifyFailure requests that a DSN be issued on delivery failure
-	// See: https://www.rfc-editor.org/rfc/rfc1891#section-5.1
+	// DSNRcptNotifyFailure requests that a DSN (Delivery Status Notification) is issued if delivery of
+	// a message fails.
+	// https://datatracker.ietf.org/doc/html/rfc1891/#section-5.1
 	DSNRcptNotifyFailure DSNRcptNotifyOption = "FAILURE"
 
-	// DSNRcptNotifyDelay indicates the sender's willingness to receive
-	// "delayed" DSNs. Delayed DSNs may be issued if delivery of a message has
-	// been delayed for an unusual amount of time (as determined by the MTA at
-	// which the message is delayed), but the final delivery status (whether
-	// successful or failure) cannot be determined. The absence of the DELAY
-	// keyword in a NOTIFY parameter requests that a "delayed" DSN NOT be
-	// issued under any conditions.
-	// See: https://www.rfc-editor.org/rfc/rfc1891#section-5.1
+	// DSNRcptNotifyDelay indicates the sender's willingness to receive "delayed" DSNs.
+	//
+	// Delayed DSNs may be issued if delivery of a message has been delayed for an unusual amount of time
+	// (as determined by the MTA at which the message is delayed), but the final delivery status (whether
+	// successful or failure) cannot be determined. The absence of the DELAY keyword in a NOTIFY parameter
+	// requests that a "delayed" DSN NOT be issued under any conditions.
+	// https://datatracker.ietf.org/doc/html/rfc1891/#section-5.1
 	DSNRcptNotifyDelay DSNRcptNotifyOption = "DELAY"
 )