Sure thing. When the user wants to send an email, this needs to happen on a button click, right? If you are using Rules on that button, there is an action that sends the email. You can add a hidden boolean node called IsEmailing and make it default to FALSE. When the user clicks the button:
1. Set IsEmailing to TRUE
2. Send email via the data connection
3. Set IsEmailing back to FALSE
You can then use IsEmailing in conditional formatting, for example, to hide the SSN field when IsEmailing=TRUE.
Hope this helps!