If you need to save all the seperated data, here's a technique using an 'array of arrays'
If you're OK with case-sensitive data, then you could use the index method as shown in TedPride's post

use strict;
my @mail_item = ();
my $i = -1;
## open FIL ......
## while <FIL> {....
while (<DATA>) {
    chomp $_;
    if (/^from/i) { $i++; }
    push @{ $mail_item[$i] }, $_;
}
## close FIL;

use Data::Dumper;
print Dumper(\@mail_item);

__DATA__
From: name1@domain.com time_sent1
 From: name1@domain.com
some content1
From: name2@domain.com time_sent2
 From: name2@domain.com
some content2
From: name3@domain.com time_sent3
 From: name3@domain.com
some content3
From: name4@domain.com time_sent4
 From: name4@domain.com
some content4
[download]