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What is the difference between DNSBL check on connect and Mail Clause


I have configured the GMS Anti-Virus option to Check incoming messages against a DNS based black list (DNSBL). I am unsure what the difference is though between these two options:
Check on Connect
Check on Mail Clause


Check on connect
As soon as a remote machine connects to SMTP on your Gordano server, the IP address of that remote machine is sent to the DNSBL server. The DNSBL server then responds saying whether or not the IP address is in its list of known open relays. If it is in the list the Gordano server will terminate the connection immediately. Otherwise the transaction will continue as normal.

Check on Mail Clause
This option makes exactly the same check using the remote servers IP address. The difference is that with this option the IP address is not checked with the DNSBL list until the remote server has issued the protocol Mail From: statement. This gives other anti-spam configurations the chance to be implemented before the RBL check. For example the Banned Hosts check in GMS Anti-Spam or other checks made at the EHLO/HELO protocol stage.

See Also:

Keywords:DNSBL Mail Clause Black List

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