Here is one way, with a cheesy flag:

use strict;
my $textfile = "iwn.txt";
open (TEXT, "$textfile") || die "Con't Open $textfile";
my @text=<TEXT>;
close(TEXT);

my $flag = 0;
foreach (@text) {
    if (/Email address:/) {
        print;
        $flag = 0;
    }
    if (/Message-Id:/ and !$flag) {
        print;
        $flag = 1;
    }
}
[download]

Jeff

R-R-R--R-R-R--R-R-R--R-R-R--R-R-R--
L-L--L-L--L-L--L-L--L-L--L-L--L-L--