I am trying to do this as well. I had thought about using a text box to allow the user to specify the To: address. The problem there is that you don't get Outlook's auto-complete / validation capabilities. As someone enters an address in Outlook, the application will provide recipient suggestions as you type; and if you enter an incorrect address it will pop up the "Check Names" dialog to let you know that it doesn't recognize your entry.
When using a standard text box, I assume you don't get these features and if an address is entered incorrectly, there would be no validation. For this reason, I would like to press the submit button, and have it do exactly what the File..Send to Mail Recipient option does.. This seems to me to be something very simple to do, but I can find nothing definitive as to how to make it happen, other than sending keystrokes which is not something I would prefer to do (assuming it's even possible in Infopath anyway), but will if I have to.
Any ideas? Thanks in advance.