[GH-6366] Add functionality to disable Authentication when connecting to SMTP (#6639)

* Issue #6366: Add feature to disable auth for Encrypted connections to SMTP settings.

* Clean PLAIN AUTH Option

* Reorder SMTP server setup and change helptext

* remove unneeded setting and modify logic

* text description change

1 files changed, 9 insertions, 13 deletions

diff --git a/utils/mail.go b/utils/mail.go
index 4b3102424..41011d67e 100644
--- a/utils/mail.go
+++ b/utils/mail.go
@@ -6,13 +6,14 @@ package utils
 import (
 	"crypto/tls"
 	"fmt"
-	l4g "github.com/alecthomas/log4go"
-	"github.com/mattermost/platform/model"
 	"mime"
 	"net"
 	"net/mail"
 	"net/smtp"
 	"time"
+
+	l4g "github.com/alecthomas/log4go"
+	"github.com/mattermost/platform/model"
 )
 
 func encodeRFC2047Word(s string) string {
@@ -59,22 +60,17 @@ func newSMTPClient(conn net.Conn, config *model.Config) (*smtp.Client, *model.Ap
 		}
 	}
 
-	auth := smtp.PlainAuth("", config.EmailSettings.SMTPUsername, config.EmailSettings.SMTPPassword, config.EmailSettings.SMTPServer+":"+config.EmailSettings.SMTPPort)
-	if config.EmailSettings.ConnectionSecurity == model.CONN_SECURITY_TLS {
-		if err = c.Auth(auth); err != nil {
-			return nil, model.NewLocAppError("SendMail", "utils.mail.new_client.auth.app_error", nil, err.Error())
-		}
-	} else if config.EmailSettings.ConnectionSecurity == model.CONN_SECURITY_STARTTLS {
+	if config.EmailSettings.ConnectionSecurity == model.CONN_SECURITY_STARTTLS {
 		tlsconfig := &tls.Config{
 			InsecureSkipVerify: *config.EmailSettings.SkipServerCertificateVerification,
 			ServerName:         config.EmailSettings.SMTPServer,
 		}
 		c.StartTLS(tlsconfig)
-		if err = c.Auth(auth); err != nil {
-			return nil, model.NewLocAppError("SendMail", "utils.mail.new_client.auth.app_error", nil, err.Error())
-		}
-	} else if config.EmailSettings.ConnectionSecurity == model.CONN_SECURITY_PLAIN {
-		// note: go library only supports PLAIN auth over non-tls connections
+	}
+
+	if *config.EmailSettings.EnableSMTPAuth {
+		auth := smtp.PlainAuth("", config.EmailSettings.SMTPUsername, config.EmailSettings.SMTPPassword, config.EmailSettings.SMTPServer+":"+config.EmailSettings.SMTPPort)
+
 		if err = c.Auth(auth); err != nil {
 			return nil, model.NewLocAppError("SendMail", "utils.mail.new_client.auth.app_error", nil, err.Error())
 		}