"The SMTP server does not support authentication"

Question:

I just upgraded to version 10.8 and emails are no longer flowing. The error I get when I test the SMTP connections is:

Here's what happened. We used to have a setting "Use SMTP Authentication" in addition to having "username/password" for SMTP. Lots of users were confused by this UI, like you could specify a username/password combination, but then disable the "Authentication" toggle.

So instead, we have removed this confusing checkbox and just check - if there's a username/password combination specified, then we use authentication, if there isn't - we don't

This worked fine on our SaaS version, but apparently, some self-hosted clients had username/password specified, BUT the "use authentication" was disabled.

Sorry about that. We should've done better.

TL;DR - the solution:

Simply clear out the "username" field in the SMTP settings and it should work again.