Email is not sending from Microsoft Outlook Issue

Support and Discussion
1

Hi,
I’m running CyberPanel on a VPS with Postfix/Dovecot mail setup. Everything works fine — I can send and receive emails using Webmail, Thunderbird, Gmail SMTP relay, and Mautic. However, when I try to send emails using Microsoft Outlook, I consistently get this error:

Technical details

SmtpSubmissionPermanent5XXException: Smtp submission failed. 
Server 'tryegbookkeeping.com' Port '587'. --> 
Unexpected SMTP server response. 
Expected: 334, actual: 535, whole response: 535 5.7.8 
Error: authentication failed: Invalid authentication mechanism 
Failure code: 1d2e

I’ve tested all combinations:
• Port 465 with SSL/TLS → fails
• Port 587 with STARTTLS → fails
• Port 25 with no encryption → fails
Thunderbird works perfectly with the same credentials and server settings.

Cyperpanel Version Info:

## Version Information

Current Version 2.4

Build 4

Current Commit 30249bb9833571d8a349a8da8b27ca7178800906

Latest Version 2.4

Latest Build 4

Latest Commit 30249bb9833571d8a349a8da8b27ca7178800906
2

I can also send and receive emails using webmail, however all my emails notifications for all my Opencart websites stopped working after recent updates, I tried both Mail and SMTP protocols, none of them works