Our outgoing mail system uses a set of rules to determine if the mail should be let through or not.
These rules are as follows:

Mail will be blocked if:

1. You try to connect to the mail server more than 50 times in 30 minutes.
2. You try to send to more than 300 recipients in 1 email per 30 minutes.
3. The message you sent was larger than 55MB which includes the message and all attachments.
4. Your connection is being blocked due to an abuse complaint.
5. The person you are sending to has been banned due to an abuse complaint.