I should have mentioned that this technique was working for the form when it was published as am InfoPath Filler form. It stopped working when I published as a web browser form due (end users on different versions of InfoPath). The emails fail to trigger.
concat(substring-after(AccountId, "\"), "@domain.com") The Account ID returned DOMAIN\userID.
As a rough work around I created the following fields:
Full Name: DisplayName (of person picker control)
First Name: substring-after(IssuerFullName, ",")
Last Name: substring-before(IssuerFullName, ",")
Email suffix: @domain.com
IssuerEmail: concat(IssuerFirstName, Dot, IssuerLastName, santos.com)
I changed the data connection to send to IssuerEmail, and this works.
Only problem is some people have a middle initial in their email address. I've added the email text field to the form and invited users to edit if necessary.
If you know of any better way I'd really appreciate hearing about it.