For email delivery fails, it is necessary to ensure that Email Gateway Defense does not retry the mail continuously. This can result in our service being blocked by the destination domain. Instead, Email Gateway Defense will return a cached response to the sender for a period of time, determined by the type of delivery failure (or success).
A delivery response is live or cached based on what Email Gateway Defense posts in the Message Log details page.
Examples of live responses (5xx responses can vary):
- Rejected (mail.somedomain.com:25:530 5.7.1 Client was not authenticated(at FROM))
- Rejected (153.43.187.93:25:530 5.7.1 Client was not authenticated(at FROM))
Example of a cached response:
- Rejected (530 5.7.1 Client was not authenticated (at FROM))
Note that a cached response will not show the destination mail server.
These are the time limits on the Email Gateway Defense caching service:
- 2xx (inbound/outbound) – 1 hour
- 4xx (inbound) – 5 minutes
- 4xx (outbound) – 20 minutes
- 5xx (inbound/outbound) – 30 minutes