I receive the message “Domain my_domain.gr has exceeded the max defers and failures per hour”. What does this mean?
If you receive an error message like this “Domain my_domain.gr has exceeded the max defers and failures per hour (5/5 (100%)) allowed”, means your outgoing mail has enabled a server rule, that will not allow you to send more emails. This occurs when a domain sends emails that are either rejected, or enter at a pending state from the recipient. The server allows a certain limit of such messages per hour. If this percentage is exceeded, then the server shall not send other emails for the rest of the remaining time (1 hour).
This error occurs in hourly basis from the server monitoring system and this limit is renewed every hour. For example, if your domain was blocked on 14:00, then you will be able to send messages again on 15:00