Ask MeCha: mom's having email probs. Emails my mom sends have the receiver as the reply to. WTF?→[More:]

Emails my mom sends out have the receiver's email address as the reply to address (so, when you hit reply to her email, the email you send comes back to you and not her).

Anyone ever heard of such a thing? I thought at first it may be a setting in her mail app (OS X Mail), but that wouldn't make sense as the reply to always changes to the person you're mailing rather than a fixed setting that isn't my mom.

Could this be a prob with her ISP? If not, what else could it be?