InfoPath Dev

I have an infopath form that automatically sends an email when the user chooses to "submit for approval".  Based on who the user selects as their approver, an email is sent to that person.  The user selects the approver from a drop-down box that contains approvers names (i.e. John Doe).  I have someone in my department that gets an error when he selects a particular approver.  The error states that infopath was unable to resolve the users name when trying to send.  However, when I perform the same actions, the form gets sent.  I've tried using user names and first name/last name and the issue is the same.  Any thoughts or suggestions?

Is it supplying a full email address (i.e. [email protected]) or just a user alias (i.e. user)? Makes a difference. The user alias can be used on corporate domains where the email system auto-resolves them, but outside of that, you will probably need to have full email addresses so there's no resolving issues.

It is always best to have full email addresses anyway. Even corporate email can have issues with just aliases.