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Override Default Settings: By default, when greylisting is enabled, all incoming messages are subject to greylisting unless you have specifically excluded them by setting other options. You can change this behavior so that no message will be greylisted unless it meets a specific criteria.


Greylist when HELO is not a fully qualified domain name: When a connection is requested from a remote server, they are supposed to identify themselves by sending a HELO (or EHLO) command along with a fully qualified domain name. If they do not, and they are not specifically excluded from greylisting, selecting this option will trigger greylisting for the particular message.


Greylist when HELO does not have a sub-domain: Many servers specify their HELO domain as something like, rather than simply The second example,, would trigger greylisting.



This option may not always be a reliable indicator that a message has a higher than normal probability of being a spam message.


Greylist when remote server has no Reverse DNS entry: If a connection has no Reverse DNS entry, greylisting will be triggered. This requires that REVDNS lookup be enabled.


Greylist when reverse DNS entry times out: If Alligate times out attempting to get a REVDNS entry for a connection, greylisting will be triggered. This would likely indicate that there is no REVDNS entry for the address. This requires that REVDNS lookup be enabled.


Greylist when sender has ADDRSPACE violations: Spammers frequently improperly format the sender or recipient name when sending a spam message. Alligate can detect this during the SMTP conversation. Selecting this option will cause messages that use this improper formatting to be greylisted.


Greylist when sender sends lowercase commands: Virtually all mail servers send SMTP commands in upper case. If commands are received in lower case, the odds are high that it may be a spam message and greylisting will be forced if this option is selected.


Greylist when sender is from an MXRate selected country, and Tarpit instead of block is enabled: This option forces a message that meets this criteria to be greylisted.


Greylist if MAIL FROM has no MX record: The domain name of the MAIL FROM sender is checked to see if it has an MX record. If it does not, greylisting will be invoked. The A record is not checked. RFCs specify that an MX record is not absolutely required, and that if a domain is missing an MX record, the A record should be used. This test is provided on the assumption that properly configured email servers should have an MX record for hosted domains.


Greylist when not an MXRate Good Sender: If the results of the MXRate lookup for the message indicates the sender is not a known good sender, greylisting will be enforced.


Greylist if MXRate Probability is greater than "xx": This option will force greylisting if MXRate reports a spam probability of "xx" percent or higher.



None of these options will cause a message to be rejected. They will only cause greylisting to be invoked for the message if and only if the message meets any or all of the criteria specified. They are all safe to use, and with the exception of Greylist when HELO does not have a sub-domain, all options will are fairly reliable indicators of spam likelihood.