exit codes are wrong

[teleshoes]

1 is returned on success and on the two most common errors. 0 is returned on all other errors.

perhaps you should revert 3545319, going back to 'return 1' for success, and 'return 0' for error.
then simply do this:

my $smtp_success = run_smtp;
my $exit_code = $smtp_success ? 0 : 125;
exit $exit_code;