Ticket emails only - data not accepted

[Louis Switch My Server]

Hi,

We have SMTP setup for Office 365 on our WHMCS, all other emails send and receive fine, however ticket emails get this error:

Email Sending Failed - Email Sending Failed: SMTP Error: data not accepted. 

Why is this and why only ticket emails we can see at present?

Thanks

Edited October 19, 2021 by Louis Switch My Server

[Louis Switch My Server]

Debug shows: SMTP Debug: SMTP ERROR: QUIT command failed

Sending emails directly to clients also works fine, is something in the emails O365 doesn’t like?

[WHMCS John]

Hi there,

The common causes for this error are outlined here: https://help.whmcs.com/m/troubleshooting/l/1261469-troubleshooting-email-sending-problems#data-not-accepted

Please check that your SMTP user can send as the support department address.