From 15b9ddf0675fbceeff3091248030eea511df2bc2 Mon Sep 17 00:00:00 2001
From: Winni Neessen <wn@neessen.net>
Date: Tue, 1 Oct 2024 17:23:29 +0200
Subject: [PATCH] Refactor error handling for non-TLS SMTP connections

Introduce a global error variable for non-TLS connections and update corresponding error handling across the codebase. This enhances readability and maintainability of the error management logic.
---
 client.go    | 8 +++++++-
 smtp/smtp.go | 6 +++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/client.go b/client.go
index acfeaa2..5d0e797 100644
--- a/client.go
+++ b/client.go
@@ -750,7 +750,13 @@ func (c *Client) tls() error {
 		}
 		tlsConnState, err := c.smtpClient.GetTLSConnectionState()
 		if err != nil {
-			return fmt.Errorf("failed to get TLS connection state: %w", err)
+			switch {
+			case errors.Is(err, smtp.ErrNonTLSConnection):
+				c.isEncrypted = false
+				return nil
+			default:
+				return fmt.Errorf("failed to get TLS connection state: %w", err)
+			}
 		}
 		c.isEncrypted = tlsConnState.HandshakeComplete
 	}
diff --git a/smtp/smtp.go b/smtp/smtp.go
index e834a09..0352133 100644
--- a/smtp/smtp.go
+++ b/smtp/smtp.go
@@ -36,6 +36,10 @@ import (
 	"github.com/wneessen/go-mail/log"
 )
 
+var (
+	ErrNonTLSConnection = errors.New("connection is not using TLS")
+)
+
 // 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 clients to add extensions.
@@ -572,7 +576,7 @@ func (c *Client) GetTLSConnectionState() (*tls.ConnectionState, error) {
 	defer c.mutex.RUnlock()
 
 	if !c.tls {
-		return nil, errors.New("smtp: connection is not using TLS")
+		return nil, ErrNonTLSConnection
 	}
 	if c.conn == nil {
 		return nil, errors.New("smtp: connection is not established")