Activation email not sending

Hello

A student is trying to activate their account but it is not sending. I have tested the smtp server with a test email which worked, I also created a new account and activated without any problems again.

Their email is quite long (33 characters long) could this be a problem? Is there a way to check this or change it?

For the time being I activated their account manually but it would be great to figure this out.

Also is it possible to access logs from the smtp server somewhere? I know you can do tutor local logs smtp but it would be good to have some files to look through.
Thanks!