We allow up to 400 emails to be sent out per hour per domain on our servers. This limit will not be changed for any reason. There is also a limit to the maximum recipients of any single message of 40 per message or per 60 second time frame.
Any mailing list or subscription service MUST use throttling of emails so that emails are sent out at an interval of at least 10 seconds between messages. More rules can be found here: Terms
We generally recommend you get setup with MailChimp which is a professional level mailing list manager and is free for lists of up to 2000 contacts. It will save you time, headaches and provide some good reporting stats. Check out their pricing plans.