PHPMailer连接SMTP成功但认证失败问题求助

问题概述 #

本地使用PHPMailer发送邮件功能正常，但部署到生产服务器后出现发送失败的情况。

已完成的验证操作 #

通过以下命令确认生产服务器到目标SMTP端口的连通性正常：

telnet smtp.partner.outlook.cn 587

代码实现 #

$mail = new PHPMailer(true);
$mail->SMTPDebug = 4;                      
$mail->isSMTP();                       

$mail->Host       = 'smtp.partner.outlook.cn';                   
$mail->SMTPAuth   = true;                                   
$mail->Username   = 'xxx';             
$mail->Password   = 'xxx';                           
$mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS;          
$mail->Port       = 587;                                  

//Recipients
$mail->setFrom('xxx', 'Mailer');
$mail->addAddress('xxxx', 'Me');    


//Content
$mail->isHTML(true);                                 
$mail->Subject = 'Here is the subject';
$mail->Body    = 'This is the HTML message body <b>in bold!</b>';
$mail->AltBody = 'This is the body in plain text for non-HTML mail clients';

$mail->send();
echo 'Message has been sent';

错误日志 #

2023-02-28 09:46:41 Connection: opening to         smtp.partner.outlook.cn:587, timeout=300, options=array()
2023-02-28 09:46:41 Connection: opened
2023-02-28 09:46:41 SMTP INBOUND: "220 SHXPR01CAXX.partner.outlook.cn Microsoft ESMTP MAIL Service ready at Tue, 28 Feb 2023 09:46:43 +0000"
2023-02-28 09:46:41 SERVER -> CLIENT: 220     SHXPR01CAXX.partner.outlook.cn Microsoft ESMTP MAIL Service ready at     Tue, 28 Feb 2023 09:46:43 +0000
2023-02-28 09:46:41 CLIENT -> SERVER: EHLO mysite.com
2023-02-28 09:46:41 SMTP INBOUND: "250-SHXPR01CAXX.partner.outlook.cn Hello [180.167.224.181]"
2023-02-28 09:46:41 SMTP INBOUND: "250-SIZE 157286400"
2023-02-28 09:46:41 SMTP INBOUND: "250-PIPELINING"
2023-02-28 09:46:41 SMTP INBOUND: "250-DSN"
2023-02-28 09:46:41 SMTP INBOUND: "250-ENHANCEDSTATUSCODES"
2023-02-28 09:46:41 SMTP INBOUND: "250-STARTTLS"
2023-02-28 09:46:41 SMTP INBOUND: "250-8BITMIME"
2023-02-28 09:46:41 SMTP INBOUND: "250-BINARYMIME"
2023-02-28 09:46:41 SMTP INBOUND: "250-CHUNKING"
2023-02-28 09:46:41 SMTP INBOUND: "250 SMTPUTF8"
2023-02-28 09:46:41 SERVER -> CLIENT: 250-    SHXPR01CAXX.partner.outlook.cn Hello [180.167.224.181]250-SIZE     157286400250-PIPELINING250-DSN250-ENHANCEDSTATUSCODES250-STARTTLS250-    8BITMIME250-BINARYMIME250-CHUNKING250 SMTPUTF8
2023-02-28 09:46:41 CLIENT -> SERVER: STARTTLS
2023-02-28 09:46:41 SMTP INBOUND: "220 2.0.0 SMTP server ready"
2023-02-28 09:46:41 SERVER -> CLIENT: 220 2.0.0 SMTP server ready
2023-02-28 09:46:41 CLIENT -> SERVER: EHLO mysite.com
2023-02-28 09:51:41 SMTP -> get_lines(): select timed-out in (300 sec)
2023-02-28 09:51:41 SERVER -> CLIENT:
2023-02-28 09:51:41 SMTP ERROR: EHLO command failed:
2023-02-28 09:51:41 CLIENT -> SERVER: HELO mysite.com
2023-02-28 09:51:41 SMTP INBOUND: ""
2023-02-28 09:51:41 SERVER -> CLIENT:
2023-02-28 09:51:41 SMTP ERROR: HELO command failed:
SMTP Error: Could not authenticate.
2023-02-28 09:51:41 SMTP NOTICE: EOF caught while checking if     connected
2023-02-28 09:51:41 Connection: closed
SMTP Error: Could not authenticate.
Message could not be sent. Mailer Error: SMTP Error: Could not     authenticate.SMTP server error: Called QUIT without being connected

请求帮助 #

已确认端口、用户名和密码均正确，搜索多日未找到相关解决方案，恳请提供解决建议，帮助实现PHPMailer发送邮件的功能。

内容的提问来源于stack exchange，提问作者checheyue