Few hours ago, I registered with the MusicBrainz wiki without providing an e-mail address. When I changed that to an actual e-amil address in my account settings, it said there was a PHP error in function mail(), and I did not receive any e-mail. The update of my e-mail address has been committed, though, but it remains in the state of being unveryfied; and clicking the button to re-send the verification e-mail yields the same PHP mail() error.

(This may or may not also apply to other occasions on which the wiki would want to send mails, I just did not happen to have any other occasion.)