I've run across this problem several times. I now recommend to my clients (and use in my own projects) AuthSMTP: http://www.authsmtp.com http://www.authsmtp.com

I've run across this problem several times. I now recommend to my clients (and use in my own projects) AuthSMTP: http://www.authsmtp.com http://www.authsmtp.com. I've been using them for a few years and I have never had a single outage or problem with their service. I also use them for all of my personal and work email. Their FAQ states their system is configured to allow a maximum of 50 recipients per message, though they recommend you keep it to 10: http://authsmtp.com/faqs/faq-20.html http://authsmtp.com/faqs/faq-20.html If you contact their support team, they can answer any questions regarding limits. The few times I've had to interact with them they were very knowledgeable and helpful.