+.SH EXIT STATUS
+On program exit, t-prot uses exit codes from
+.I /usr/include/sysexits.h
+and thus behaves in a manner that sendmail and others understand when
+calling t-prot.
+.sp
+Currently, the codes used are
+.RS 20
+.PD 0
+.TP
+EX_OK
+.TP
+EX_USAGE
+.TP
+EX_DATAERR
+.TP
+EX_UNAVAILABLE
+.TP
+EX_SOFTWARE
+.TP
+EX_IOERR
+.PD
+.RE
+.sp
+If, however, perl fails to compile and execute t-prot, perl's normal
+exit codes will be returned.