'-d52.100'' ''''

The -d52.100 debugging switch prevents sendmail from disconnecting from its controlling terminal device. To show that it is skipping the disconnect, it prints:

don't

This debugging switch is useful for debugging the daemon. Note that this -d52.100 prevents the detach but allows the daemon to fork(2). This differs from the behavior of the -d99.100 debugging switch (-d99.100).