$ echo "
Sender: 123

Recipient:  aaa

Date: 2009/03/04

Content: data0039

Time: 08:20:01

Operator: test

Subject: test01

Content: data data

Subject: RE: test

Content: data2 data

Additional: additional data
" | perl -ne'
if ( 1 .. $content && /^Subject/ ) {
    $content += /^Content/;
    print;
    }
'

Sender: 123

Recipient:  aaa

Date: 2009/03/04

Content: data0039

Time: 08:20:01

Operator: test

Subject: test01
[download]

Can you show us what you have so far?

I would probably read the file one line at a time, saving them as I go, and when you match what you want, print out what you have already seen (pretty much exactly as OP describes...) :

use warnings;
use strict;

open (my $fh, '<', 'test.txt') || die "Failed to open test input : $!"
+;
my $contents = '';
my $previous = 'Not set';
my $pass = 0;

while (<$fh>){
  my $line = $_;
  if ( $line =~ /^Content:/ && $previous =~ /^Subject:/ ){
    ## if we matched the previous line as a 'Subject' line
    ## and this line is a 'Content' line
    print $contents;
    $pass = 1;
    last;
  }
  
  ## append current line and set previous line
  $contents .= $line;
  $previous = $line;
}
print "No match found.\n" unless $pass;
close $fh || die "Failed to close test file : $!";
[download]

I know this is verbose, but KISS works well for me...

learningperl01 you described in words pretty much exactly as I have done, and broke the problem down into the component parts well, so maybe have a go next time! If you are having problems with regexes, then check out perlre

Update: Disclaimer! Code not tested!