I like that it's easy to set up rules for different types of emails (ie newsletters).
It also has great support if something goes wrong! The only thing about correct.emails which could be improved would probably have more options in terms of what type of links can go through - eg nofollow or do follow etc? But this isn't really their fault as they don't create them so not sure why there are limitations with link creation here but still very good product otherwise!! We've been using correctly.mails since we launched our newsletter last year & haven't had any issues at all with spam filters either from other providers/senders who send us bulk mailings.