Some people opt to get email notifications when someone in the forum sends them a Private Message. These email notifications include the entire text of the PM and sometimes people erroneously reply to the email notification rather than checking their PMs and then replying to the PM. Instead of going where you think it will, it goes to me since the email notification is sent by the forum software. Nobody has yet to divulge any juicy tidbits that would sear my tender eyeballs but all the same, your message is not being seen by the intended recipient.
Some days I have time to return these errant emails to the sender and some days I don't. So be careful to not respond to an email notification of PMs.