This document collects issues that came up in the past, and that cannot be solved in pretalx with a reasonable amount of effort or time.
We run into issues when using Gmail. In Google’s eyes, pretalx is a less secure app, which you’ll have to grant special access. Even then, Gmail is known to unexpectedly block your SMTP connection with unhelpful error messages if you use it to send out too many emails in bulk (e.g. all rejections for a conference) even on GSuite, so using Gmail for transactional email is a bad idea.