Having just set up a new smartphone running Windows Mobile connecting to Microsoft Exchange we found that the default option on incoming emails was ‘reply to all’ even if the email had only one sender and recipient.

If you selected reply to all and replied the reply was sent to the sender of the original message but also back to yourself.

After a lot of head scratching we found that besides specifying the Exchange account in the mail account settings we also had to enter the email address in advanced settings. Seems that Windows Mobile has to know your email address even if you’re sending/receiving through Exchange so that it can determine that you are the recipient of the email and not include you in any replies you send back.