#!/usr/bin/env perl

use strict;
use warnings;
use feature qw(say);

my @strings = (
    'From: John Doe <peter@piper.com>',
    'From: John Doe <john@doe.com>',
    'From: John Doe',
);

foreach my $string (@strings) {
    if ($string =~ m/^From:\s+John\s+Doe(?!\s+<john\@doe\.com>)/) {
        say "BAD: $string"
    }
    else {
        say "GOOD: $string"
    }
}