Strange that it does so only when you first open it.
Try eliminating that initial mail check:
Tools, Options, General, uncheck "Send and receive messages at startup".
The password stored in windows mail does not match the one stored on the
email server. If you know the correct password for you email account you can
change it in Windows Mail by clicking on Tools then Accounts then selecting
the account on Internet Accounts (such as pop.domain.com ) then click on
properties then click on the servers tab. On the servers tab you will see the
Password field, delete what is there and enter the correct password. click on
OK and close and send/receive all.
