I'd do something like the following (untested)
my @msg;
push @msg, "$currentlist_file too old" if ( -M $currentlist_file > 1);
push @msg, "$pre_historical_file too old" if ( -M $pre_historical_file
+ > 2);
if (@msg) {
open(my $mail, '|-', "/usr/bin/mailx ...") or die "failed opening
+pipe to mailx";
# salutation and valediction :-)
unshift @msg, 'Dear Steve,', '';
push @msg, '', 'I beg to remain, Sir, your most humble and obedien
+t servant,', "\t$0";
print $mail, join ("\n", @msg);
close $mail;
}