If the layout is fixed (that is if the data changes but the position of the data does not change, then try this:
$_='May 2 04:06:15 lon.mail.net exim[17905]: 2012-07-03 07:06:15 1SPP
+tO-0004en-PS <= me@ours.co.uk H=smtpout.mail.com [22.5.10.4] I=[6.5.1
+4.4]:25 P=esmtp S=13333 id=6aeca3b79b8892d6105dab131c76f066@localhost
+.localdomain T="Half price offer"';
my @data= split(/ /);
my $Email=$data[10];
my $IP=$data[12];
$IP=~s/\[//g;
$IP=~s/\]//g;
print "Email: $Email\n";
print "IP: $IP\n";
As you are limited to Perl 5.8.4, regex's are not as fast as in 5.10 and up so I would try to limit the data I perform a regex on as you never know what will change and cause your program to bomb (usually at 3:00am on a Sunday morning). I would split your data into its many parts and then run what ever regex you need on a smaller data chunk. For the email you don't even need a regex. The square brackets can be removed in any number of ways, I choose the lazy way in my example.
