Outlook generates error code 0X80040201 when sending mail. The email sits in the outbox indefinitely.

This error may occur when a computer that was previously part of a Microsoft Exchange environment tries to send email to an address that was part of the same Exchange server, but has been removed. As a result, Outlook tries to send an email to the alias or nickname associated with the recipient, instead of the valid email address for that particular recipient.

Update all entries in your address book that were formerly part of your Exchange setup by ensuring that all related entries have a full, valid email address. Alternatively, just remove the contact from your contact list.