InfoPath Dev

Have a Employee form where the persons (new) company email address gets created in a separate textbox (EmailAddress) captured from the "FirstName" textbox and "LastName" textbox with the: concat(EmpFirstName; "."; EmpLastName) e.g. [email protected] How can I check (towards exchange) if this email address can be used to the new employee and isn’t already assigned to another person?

It sounds like you need a custom Active Directory web service that uses an LDAP connection string to query your company's active directory, and return a result that indicates whether the email address is already assigned to another person.

I don't know of anything in InfoPath or SharePoint that allows this. It would probably be a custom-made web service.