If you are bothered by differences in upper-case/lower-case use of the headers, why don't you normalize all header names extracted from the eamil to lower-case and check against the lower-cased name of the header?

There are lot of modules to handle email messages on CPAN, you can start with MIME::Tools, Email::MIME, and Date::Parse.

CountZero and zwon have provided guidance on parsing the headers. This expands on zwon's referral to Date::Parse.

#!/usr/bin/perl
use warnings;
use strict;
use Date::Parse;

# 799107 

my $data = '';

while ( <DATA> ) {
    # print $_;
    $data = $_;
    chomp ($data);
        if ($data =~ /^DATE:\s+(\w{3}, \d+ \w{3} \d{4} \d\d:\d\d:\d\d)
+ ([+-]\d{4})/ ) {
        my $date = $1;       # Don't do this; check existence of $1 
        my $zone = $2;         # and $2 before you try to use them!
        print "'Date' found: $date which converts to: ";
        my $time = str2time($date);
        print "$time Zone Offset: $zone\n";
        print "\t Restringified: " . localtime($time) . "\n"; # reconv
+ert, solely as a check on above
    }
}

=head OUTPUT
'Date' found: Sat, 9 Feb 2008 17:14:18 which converts to: 1202595258 Z
+one Offset: -0730
         Restringified: Sat Feb  9 17:14:18 2008
'Date' found: Sun, 10 Feb 2008 04:23:55 which converts to: 1202635435 
+Zone Offset: +0400
         Restringified: Sun Feb 10 04:23:55 2008
=cut

__DATA__
SUBJECT: test
FROM: John Smith
DATE: Sat, 9 Feb 2008 17:14:18 -0730
TO: Joe Doe
additional for demo only
DATE:  Sun, 10 Feb 2008 04:23:55 +0400
[download]

You could also roll your own, if for some unreasonable reason you want (not recommended) to avoid using an email module. Read on:

And, just BTW, you probably meant "disparate" rather than "desparate."
  :-)

Woops! "disparate" is should be :blush: but maybe it goes to show you the state of mind I was in when I posted the thread :-D

Well, to answer some of my own questions :

1. MIME::Parser is way too heavy for this purpose. If you have to call $parser->filer->purge(); to delete all the files created from each of the mails. This really seems too much to "just read 4 fields from an email header".

MIME::Head however seems to fit the bill very well :

my $head = MIME::Head->read( \*FILE ); # TODO : Does it read the WHOLE
+ email or skips the remaining mail after reading the header?
$head->unfold;

# Was a "Subject:" field given?
# $subject_was_given = $head->count('subject');

print $head->get('subject');
print $head->get('Message-ID');
print $head->get('from');
print $head->get('date');
[download]

2. I would appreciate some answers to this.

Of course missing id's will be logged and error handling done, but I was wondering if there are any servers with such known behaviour.

3. This works just dandy :

use Date::Manip;
Date_Init("ConvTZ=IGNORE","TZ=GMT");

my $date = UnixDate( $head->get('date') , '%Y_%m_%Q-%H%M%S');
print $date;
[download]

This can convert, for eg : "Sat, 9 Feb 2008 17:04:08 EET" to "2008_02_20080209-170408"

Thanks guys for the great insights! Furthur tips/tricks/etc are welcome though.

2. Is there any possibility where a "Message-ID" is not part of the mail header?