During the install of NMS TFMail Autoinstall, it is important, I mean REALLY important to pay attention during the install process when it tells you, in red text no less, that the email address you enter for postmaster must be valid. Not as in “Oh, I’m sure that that email is valid, of course it is, I won’t bother to check”, but as in “Actually Being Valid Since I Actually Checked It IS Valid”. Because, if it isn’t valid you get

“Application Error
An error has occurred in the program

close sendmail pipe failed, mailprog=[/usr/bin/sendmail -oi -t] at (eval 6) line (something)”

acting all innocent like it was you setting the wrong path for sendmail, even though you set it right, and even though you spent AGES* checking that it was set right, and reinstalling multiple times, and screaming a lot.

If you are using TFMail Autoinstall, doublecheck that you have supplied a valid, working email address for the Postmaster during the install.

*AGES is a very very long time**.
** whimper.