You’re obviously posting it to a mailbox that WordPress is accessing, so check the mailbox that your friend has sent an email to, if the email is still in there then WP hasn’t taken it out and thus your email settings in WP are probably wrong. If the email isn’t in there your friend has probably sent it to the wrong address, not sent it at all or WP may not have read it correctly.
This is just the first step into determining the problem, tell us how you get on.