Bizarre!

I've got a sendmail server running on my mail server. It has been working fine until a few days ago when it started delivering two copies for each message for one particular user. Incidentally only that user is aliased meaning the email address isn't a real user on the mail server but that is probably irrelevant as I've tried to send email to the REAL username for that user and same thing happened.

I've checked /var/log/maillog and there is log for only one message being sent but the file /var/spool/mail/xxxxx for that user always have two messages so it can't be the pop daemon as well. My instinct is it gotta have something to do with sendmail. I've tried removing aliases for that user anyway, tried sending messages to/from other users in same domain and from outside but same problem. To sum it up: It sends exactly two messages everytime to only and only that user whenever I send one message to him.

Anyone out there?

Thanks for help in advance.