Sometimes when I send an email it shows up to the recipient as being from a unassociated email (still one of mine however) and on the chance that they receive the email from the correct address, if they reply to it the reply will go into the other email and not to the address I sent it from.  The two emails are in no way related to each other except they are both mine.  I don't understand this and I have missed several important emails because I didn't realize they were not at the right address.