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. 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:
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.
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
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.