If Encryption Management Server cannot make outbound http connections, an inbound message that is S/MIME signed and/or S/MIME encrypted, is deferred. The sending mail server therefore keeps trying to send the message. This occurs even though the inbound message is successfully processed by Encryption Management Server and successfully passed to its Inbound mail proxy.
The result is that the recipient receives the same message multiple times.
Encryption Management Server 3.3 and above.
In a configuration such as this:
Internet -> Postfix mail server -> Encryption Management Server -> Microsoft Exchange Server
This error appears in the mail log. The message is proxied successfully to the Exchange Server but the transmission channel from the Postfix mail server is not closed properly: 2018/04/20 15:28:36 +01:00 NOTICE pgp/messaging: SMTP-00000: passing through unmodified
2018/04/20 15:28:36 +01:00 ERROR pgp/messaging: SMTP-00000: error handling SMTP DATA event: write failed
2018/04/20 15:28:37 +01:00 ERROR pgp/messaging: SMTP-00000: pgpproxy: error reading/processing message error=-11989 (write failed)
When Encryption Management Server processes an S/MIME signed and/or encrypted message, it checks whether the certificates that it observes in the mail flow are revoked. This, clearly, is best practice; revoked certificates should not be used.
There are two mechanisms used to check whether S/MIME certificates are revoked:
CRL (Certificate Revocation List). The list is downloaded from a remote host. Encryption Management Server can only process CRL files that are under 1 MB in size.
Both mechanisms require that the host checking the certificates can connect over http to a remote host.
If Encryption Management Server cannot make outbound http connections it causes problems with S/MIME mail processing.
There are two possible solutions to this issue:
Ensure that Encryption Management Server can make outbound http connections. This is the preferred solution because it is clearly best practice to check whether S/MIME certificates are revoked and this can only be done using outbound http connections.
Configure Encryption Management Server to check certificate revocation status using only CRL and not OCSP. This configuration option is available only in Encryption Management Server release 3.4 MP1 and above. Please contact Symantec Technical Support if you wish to use this option. Note, however, that Encryption Management Server can only process CRL files that are under 1 MB in size.
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