I use PHPmailer, and the "to" address format (line 416 in "abuse.admin.inc", function abuse_admin_warn_user) causes an error, so no e-mail has been sent. Apparently, PHPmailer doesn't recognize the address formatted like this:

$to = check_plain($account->name) ."<$account->mail>";

Of cause the same error will happen if I use "warn and remove", since the same function is in use.