OAuth2 for SMTP

elij

I've configured OAuth2 for Remote Mailbox, and that seemed to work well. However, now when trying to dial in the SMTP settings, I am having a lot of issues. I tried configuring SMTP authentication as "Same as Remote Mailbox" and every time I saved that configuration, the page would crash. I pulled the logs from Apache, below is the error I am receiving now when attempting to send a test email.
sh: 1: /usr/sbin/sendmail: not found

elij

Whenever I attempt to change the settings and save, this is the error I receive on Outgoing settings. Even though I am not attempting to utilize STMP auth.
5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant. Visit https://aka.ms/smtp_auth_disabled for more information. [SA1P222CA0031.NAMP222.PROD.OUTLOOK.COM 2026-05-27T17:59:10.662Z 08DEBB8E215F9923]

KevinTheJedi

elij

First issue sounds like a fatal error which should be logged in your PHP error logs. Second issue sounds like Authenticated SMTP is disabled in your tenant and/or at the mailbox level. Contact your mail admin to have them double check that and enable if disabled or add exception for the one user (or any mailbox you will be configuring SMTP for).

Cheers.

elij

Below are the only errors I see in the log. Am I not looking at the correct log?

[Wed May 27 17:49:35.120302 2026] [mpm_prefork:notice] [pid 2326] AH00170: caught SIGWINCH, shutting down gracefully
[Wed May 27 17:49:35.210466 2026] [mpm_prefork:notice] [pid 2641] AH00163: Apache/2.4.58 (Ubuntu) OpenSSL/3.0.13 configured -- resuming normal operations
[Wed May 27 17:49:35.210507 2026] [core:notice] [pid 2641] AH00094: Command line: '/usr/sbin/apache2'
sh: 1: /usr/sbin/sendmail: not found
sh: 1: /usr/sbin/sendmail: not found
sh: 1: /usr/sbin/sendmail: not found
sh: 1: /usr/sbin/sendmail: not found

Also, I have configured to allow authenticated SMTP for this user still does not resolve.

KevinTheJedi

elij

No, that looks like the webserver (apache) error logs. You need to find your PHP error logs.

It does take some time for the changes to take affect. You can also try disabling it, saving it, re-enabling it, and saving it. That sometimes helps speed things up.

Cheers.

elij

Okay i think that got it working. However, I tested creating a ticket from email, and it states there is a new ticket but I cannot see it. It is hidden from the ticket queue.

elij

Never mind, figured that one out too. It was populating under a queue that the agents didn't have access to. Thanks for the tips. Waiting for SMTP auth to take was the fix.