`Don't take two steps forward and one step back`

Here's some code I wrote myself in an article about spam processing:

        http://www.linuxplanet.com/linuxplanet/tutorials/1096/4/

The header of an email message is in $header:

     Received: from renoir.op.net (root@206.84.208.4) 
       by plover.com with SMTP; 10 Apr 1997 05:08:31 -0000 
     Received: from major.globecomm.net (major.globecomm.net [207.51.48.5]) 
       by renoir.op.net (8.7.1/8.7.1/$Revision: 1.10 $) with ESMTP id BAA02191 
       for <mjd@op.net>; Thu, 10 Apr 1997 01:06:35 -0400 (EDT) 
     From: LRS@getstartednow.com 
     To: friend@public.com 
     ...

We want to split this up into lines and put them in a hash
But this doesn't work:

        @lines = split /\n/, $header;

Because some of the logical lines are broken across two physical lines