If your email is returned with error messages similar to the following, you may have sent too many bounced or deferred messages within one hour.
Domain has exceeded the max defers and failures per hour (5/5 (100%)) allowed. Message discarded.
To avoid misuse by spammers and subsequent blacklisting of the server in spam databases, all email errors are tracked.
If more than 50% of email sent from a particular domain within one hour is bounced or deferred by the recipient server, a temporary block on sending additional email will be activated for that domain. After the hour has passed, this block will be automatically lifted.
- Bounced: Any email messages that are returned with an error status.
- Deferred: This usually indicates that the message could not be delivered to the recipient's server, but that additional attempts will be made. In most cases, email servers will attempt to deliver deferred messages several times over a 24 hour period. If the receiving email server becomes available again within this time period, the message will be delivered.