The NEW & Improved system works like this
When ESS/CPL gets back an "unknown error" from ATD the mail will be scanned normally by ESS and if not blocked for some other reason it will be quarantined.
A Block/Quarantine SMTP response will be returned to the sender.
The mail will show in the users quarantine log (if they have an account)
The message will show in the message log with the reason "ATD Service Unavailable"
NOTE: Mail quarantined for "ATD Service Unavailable" cannot be manually delivered by the user. Only the admin can deliver this mail by OPENING it from the main message log and clicking the deliver button. When delivery is attempted a warning popup will display warning the admin that this message may contain a virus and asking them to accept the potential risk of delivering the mail.
Email Delivery Warning:
One or more attachments could potentially have advanced threats that may harm your
system. Only deliver the message if you are expecting it and are sure there are no threats
or viruses. Contact your administrator for more information.
[ ] I accept that Barracuda assumes no risk associated with threats my organization
may sustain during or in conjunction with the delivery of this message and its
If ATD can open the file but does not return the result in the normal timeout (5 seconds) then ESS/CPL will defer the connection and the sender will retry. ATD will continue to process the message in the background and if completed by the time the retry comes in the mail will be delivered or blocked depending on the result returned by ATD. This could take several retries of the message by the sender.
If the mail is processed by ATD for TOO LONG (ATD continues to return an 800 error) then after a set timeout ESS/CPL will quarantine the message following the same process as above. This timeout is currently 4 hours.
If you try to deliver mail quarantined for "ATD Service Unavailable" from the users quarantine log or from the main message log you will get this error so remember that to deliver the mail you must open the message and then click the deliver button and then accept the disclaimer.
Delivery error: This message may contain a Virus.