The EX_OSFILE exit code (value 72) results when certain system files could not be opened and when certain system programs could not be executed.

When sendmail gets a SIGHUP signal, it attempts to re-execute itself (SIGHUP). If it fails, the following error is logged and sendmail exits:

could not exec /path/sendmail: reason

The sendmail program can run a program to look up a key in a database. If sendmail fails to run the program, it prints the following error:

prog_map_lookup(program) failed (reason) -- closing 

We probably don't have to mention this, but the sendmail program has to read its configuration file. If it fails to open, stat, or read that file, or if that file is not a plain file, it prints one of the following errors (depending on your version of sendmail) and exits with an EX_OSFILE value:

cannot open
cannot fstat
not a plain file
I/O read error
filename: cannot open reason
filename: cannot fstat reason
filename: not a plain file reason
filename: I/O read error reason