I found out the hard way that by default, Amazon limits the amount of mail you can send from an EC2 instance. I don’t have exact numbers, but from my experience, I would say its around 50 messages in a month. Also worth noting is that all EC2 IP addresses are blacklisted by spamhaus1. Some providers, such as Optimum Online, will block all messages on that blacklist. You can apply to have the limits removed, as well as being removed from the blacklist by filling out a form for Amazon linked here 2.

  1. You can check IP addresses at spamhaus 

  2. From their FAQ