user1@example.com
user3@example.com
...

##</code><code>##

user1@example.com
user2@example.com
user3@example.com
USER1@EXAMPLE.COM<mailto:USER1@EXAMPLE.COM>
user4@example.com
user5@example.com
user5@example.com<mailto:user5@example.com>
...

##</code><code>##

use Modern::Perl;
use File::Slurp qw/ read_file write_file /;

my $removeList = join '|',
	map { chomp; $_ } read_file 'removelist.txt';
	
write_file 'finallist.txt',
	grep !/$removeList/i, read_file 'masterlist.txt';

##</code><code>##

user2@example.com
user4@example.com
user5@example.com
user5@example.com<mailto:user5@example.com>