Processing order seems to be the problem as Albannach points out. I haven't read his post closely, but here is a modified version of your program that seems to run correctly with a data set that I copied/modified from a sendmail inbox:

use strict;
  my $flag = '0';

  ### I had to take a few of the extra blanks out of the next three se
+arch variables
  my $from = 'From: ';
  my $full_subject = 'Subject: ';
  my $date = 'Date: ';

  my @buffer = ();
  my @spamcop_email_array = <DATA>;

open (TEXTOUT,  ">junk.out") || die "Can't open 'junk.out'";

              #loop and fill @buffer#
foreach (@spamcop_email_array){
    if(s/.*$from//){
        ### changed [0] to [1]
        $buffer[1] = $_;
        $flag = 0;
        }
    if(s/.*$full_subject//){
        ### changed [1] to [2]
        $buffer[2] = $_;
        $flag = 0;
        ### moved print from date if block to here
        print TEXTOUT @buffer;
        }
    if(s/.*$date//){
        ### changed [2] to [0]
        $buffer[0] = $_;
        $flag = 0;
        }
    }
close TEXTOUT;
__DATA__
From MAILER-DAEMON Fri Jan  4 18:04:20 2002
Date: 04 Jan 2002 18:04:20 -0600
From: Mail System Internal Data <MAILER-DAEMON@loopey.faraway.net>
Subject: DON'T DELETE THIS MESSAGE -- FOLDER INTERNAL DATA
Message-ID: <1010189060@loopey.faraway.net>
X-IMAP: 0910805650 0000003175
Status: RO

This text is part of the internal format of your mail folder, and is n
+ot
a real message.  It is created automatically by the mail system softwa
+re.
If deleted, important folder data will be lost, and it will be re-crea
+ted
with the data reset to initial values.

From root@loopey.faraway.net Sun Jun 20 10:37:57 1999
Received: from localhost (root@localhost)
        by loopey.faraway.net (8.8.8+Sun/8.8.8) with ESMTP id KAA05403
+;
        Sun, 20 Jun 1999 10:37:57 -0500 (CDT)
Date: Sun, 20 Jun 1999 10:37:56 -0500 (CDT)
From: Super-User <root@loopey.faraway.net>
To: <light@loopey.faraway.net>,
        xxxx xxxxx <joey@loopey.faraway.net>
Subject: Re: accounts for DISL (fwd)
Message-ID: <Pine.GSO.4.10.9906201036380.5380-100000@loopey.faraway.ne
+t>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Content-Length: 1064
Status: RO
X-Status:
X-Keywords:
X-UID: 263

joey,
  Looks like you may have sent Randy a note from root - here's her rep
+ly.
I'll address the SAS issues.
- Andy

---------- Forwarded message ----------
Date: Fri, 18 Jun 1999 09:01:04 -0500
From: rsch <rsch@xxxx.xxx>
To: Super-User <root@loopey.faraway.net>
Subject: Re: accounts for DISL

joey,
If possible I would like to keep my account (rsch) to run SAS jobs
for the faculty from time to time.

Thanks,
Randy

From light@loopey.faraway.net Wed Mar 28 12:05:57 2001
Date: Wed, 28 Mar 2001 12:05:48 -0600 (Central Standard Time)
From: xxxx xxxx <light@loopey.faraway.net>
To: xxx xxx xxx <joey@loopey.faraway.net>
Subject: xxxxx account
Sender: light@loopey.faraway.net
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Content-Length: 364
Status: RO
X-Status:
X-Keywords:
X-UID: 1565

joey,
  when you get a chance, could you please do whatever is necessary to
remove xxxx xxxxx xxxxx account? We will want to leave a
forwarding record in place in the aliases file.
[download]

The output file:

04 Jan 2002 18:04:20 -0600
Mail System Internal Data <MAILER-DAEMON@loopey.faraway.net>
DON'T DELETE THIS MESSAGE -- FOLDER INTERNAL DATA
Sun, 20 Jun 1999 10:37:56 -0500 (CDT)
Super-User <root@loopey.faraway.net>
Re: accounts for DISL (fwd)
Fri, 18 Jun 1999 09:01:04 -0500
rsch <rsch@xxxx.xxx>
Re: accounts for DISL
Wed, 28 Mar 2001 12:05:48 -0600 (Central Standard Time)
xxxx xxxx <light@loopey.faraway.net>
xxxxx account
[download]

While this code works in most cases, you should really beef it up with some error checking. I seem to remember a recent post that described a CPAN module that parses email. If so, you might consider switching since it might be vetted already and insure more accurate results. BTW, I guess that $flag will serve a future purpose. It doesn't seem to do anything now.

HTH,

--Jim