We send 100,000 or so emails to members through our VB forums per month. You know, email confirmation, password reset, reply notices and such - transactional emails. Currently we send all these through our dedicated server. But we find AT&T, AOL and sometimes others like to block these emails as spam. They don't put them in spam folders - they block them outright. We're looking at using a 3rd party smtp service like Sendgrid or Mandrill to correct this issue so I'd like to ask if you've used these two or others or if you have had good luck with other 3rd party mailers.