feat: 支持强制使用 AUTH LOGIN 以解决 outlook 等邮箱的发件问题 (#4112)

* feat: 支持强制使用 AUTH LOGIN 以解决 outlook 等邮箱的发件问题

* fix: 修复通过 SSL 发送邮件时绕过 AUTH LOGIN 的问题

* fix: remove redundant branch, delete test file, add i18n translations

- Remove redundant else-if branch in SendEmail since auth is already
  computed via getSMTPAuth()
- Delete option_smtp_auth_test.go as requested
- Add i18n translations for '强制使用 AUTH LOGIN' checkbox

common/constants.go

@@ -80,6 +80,7 @@ var InsecureTLSConfig = &tls.Config{InsecureSkipVerify: true}
 var SMTPServer = ""
 var SMTPPort = 587
 var SMTPSSLEnabled = false
+var SMTPForceAuthLogin = false
 var SMTPAccount = ""
 var SMTPFrom = ""
 var SMTPToken = ""

common/email.go

@@ -19,6 +19,20 @@ func generateMessageID() (string, error) {
 	return fmt.Sprintf("<%d.%s@%s>", time.Now().UnixNano(), GetRandomString(12), domain), nil
 }
 
+func shouldUseSMTPLoginAuth() bool {
+	if SMTPForceAuthLogin {
+		return true
+	}
+	return isOutlookServer(SMTPAccount) || slices.Contains(EmailLoginAuthServerList, SMTPServer)
+}
+
+func getSMTPAuth() smtp.Auth {
+	if shouldUseSMTPLoginAuth() {
+		return LoginAuth(SMTPAccount, SMTPToken)
+	}
+	return smtp.PlainAuth("", SMTPAccount, SMTPToken, SMTPServer)
+}
+
 func SendEmail(subject string, receiver string, content string) error {
 	if SMTPFrom == "" { // for compatibility
 		SMTPFrom = SMTPAccount
@@ -38,7 +52,7 @@ func SendEmail(subject string, receiver string, content string) error {
 		"Message-ID: %s\r\n"+ // 添加 Message-ID 头
 		"Content-Type: text/html; charset=UTF-8\r\n\r\n%s\r\n",
 		receiver, SystemName, SMTPFrom, encodedSubject, time.Now().Format(time.RFC1123Z), id, content))
-	auth := smtp.PlainAuth("", SMTPAccount, SMTPToken, SMTPServer)
+	auth := getSMTPAuth()
 	addr := fmt.Sprintf("%s:%d", SMTPServer, SMTPPort)
 	to := strings.Split(receiver, ";")
 	var err error
@@ -80,9 +94,6 @@ func SendEmail(subject string, receiver string, content string) error {
 		if err != nil {
 			return err
 		}
-	} else if isOutlookServer(SMTPAccount) || slices.Contains(EmailLoginAuthServerList, SMTPServer) {
-		auth = LoginAuth(SMTPAccount, SMTPToken)
-		err = smtp.SendMail(addr, auth, SMTPFrom, to, mail)
 	} else {
 		err = smtp.SendMail(addr, auth, SMTPFrom, to, mail)
 	}