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;
}
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