For email delivery fails, it is necessary to ensure that the Barracuda Email Security Service (ESS) does not retry the mail continuously. This can result in our service being blocked by the destination domain. Instead, ESS 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 ESS 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 (220.127.116.11:25:530 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 ESS caching service:
- 2xx (inbound/outbound) – 1 hour
- 4xx (inbound) – 5 minutes
- 4xx (outbound) – 20 minutes
- 5xx (inbound/outbound) – 1.5 hours