Thread:Project:Support desk/Does not send emails

My wiki does not send emails anymore. I know that it was working before the upgrade to 1.22.2, but I don't know if it ever worked after the upgrade.

Sending an email with Special:EmailUser says "Your email message has been sent.", but the email never arrives.

It is an internal wiki accessible only with an user account. Some users forgot their password and cannot change it because they don't receive the notification email.

It is installed on a managed server, I have access via cPanel, here is the Special:Version output:

Where do I start investigating?