#!/usr/bin/perl

use strict;
use warnings;

use Time::Piece;

my $format = '%b %e %T';
my $start = Time::Piece->strptime('Feb  1 10:30:00', $format);
my $end   = Time::Piece->strptime('Feb  2 10:30:00', $format);

open(FILE, "/var/log/maillog") or die "Couldn't open maillog: $!; aborting";

while (<FILE>) {
    my ($timestamp) = /(^\w+\s+\d+\s+\d\d:\d\d:\d\d)/;
    my $t = Time::Piece->strptime($timestamp, $format);

    print if $t >= $start && $t <= $end;
}

close(FILE);