Gmail External Email Highlighter

For highlighing email addresses in Gmail 'to' fields that don't fit certain rules - ie. that are being sent outside the company.

If your company uses Gmail's web client to send emails, this extension will highlight email addresses that fall outside of rules you define. This way your users can easily see if they're accidentally sending an email to someone outside of the company. Or you could just put your bosses email in to make sure you're never caught out by not noticing them in the CC box! Email rules are set using regex.