When I design a form I have two large sections: one for filling out the fields, and one to display them when emailing.
I do this because InfoPath needs some "assistance" when sending email. The fields usually don't look nicely if left alone.
So before the email is sent, a rule hides the "filling out" section and shows the "emailing" section, which I've designed to look "pretty".
In the scenario of a field with variable width, I use "Auto" as the height and this seems to work in the email views (expands as necessary).