After messing with getting sendmail to run on a fedora 24 box for a week+, I punted it and wrote a simulator that will conduct the network traffic for an SMTP transaction without actually doing anything. Debugging sendmail was making no progress, and that is not my goal anyway. The simulator is very simplistic, but should be sufficient for initial development of the SMTP client code. The simulator was a one afternoon project from some libraries that I already have written and debugged. I verified the sequence of commands and the responses from the server by telneting into my ISP's email server and issuing the command sequence to log in and send the email.
The ST module used on the first board that I built has it's antenna on the module. This will limit the case design for the board, so I built up another board with a slightly different module that has an antenna connector instead of the actual antenna. The board construction and checkout went smoothly and the new board works fine. This way, I can stick the antenna outside the case when the board is put to use.