From: Stu <stu@...>
Date: 2013-05-24T07:53:00+09:00
Subject: Re: Regular expression to find a break in a pattern

You can do you regex test against both contexts ^To: and ^From: and
use post_match to reveal the contents after:

http://ruby-doc.org/core-2.0/MatchData.html#method-i-post_match

~Stu