With my community growing remarkably large on a daily basis, we are struggling to send mass e-mails without errors! We're simply sending too many e-mails per hour (Over 3000 e-mails per hour on some days!) - our community members love being notified whenever someone replies to their post. It's a growing culture.
I'm wondering, what service do you like using to send e-mails to your users without bloating down your own server?