Not receiving email with SMTP Gmail Service

Problem Statement

We are using SMTP Gmail service as our custom email provider. We did not receive emails. The log shows the error:

Invalid login: 535-5.7.8 Username and Password not accepted.


You need to provide a Gmail App Password for some apps to allow them to connect to Gmail service since they ask for it if it is a non-google-app or a device trying to log in.

Gmail documentation guide: Sign in using app passwords - Gmail Help