Oftentimes the sending mail server's IP address will not match any known MX or A records for a given domain and yet still be delivering the mail legitimately. Finally, it is generally agreed that accepting mail from sources that identify themselves by using a domain that does not exist should be optional.
Enable this option if you want MDaemon to perform pointer record lookups on all inbound SMTP connections. If this box is checked then MDaemon will send a 501 error code (syntax error in parameters or arguments) and close the connection if no PTR record exists for the domain.
If this box is checked then MDaemon will send a 501 error code (syntax error in parameters or arguments) and close the connection if the result of a pointer record lookup fails to match. Click this option if you wish to defer the PTR lookup on inbound SMTP connections until after the SMTP MAIL command in order to see whether or not the connection will use authentication. Enabling this switch will cause a lookup to be performed on the domain name that is passed during the MAIL command portion of the mail transaction. Click this check box if you want a 501 error code to be sent and then the connection closed when the result of a lookup appears to be a forged identification.
When the result of a reverse lookup states that the server is using a forged identification, this result may frequently be incorrect.


Click this option if you wish to defer the lookup until after the SMTP MAIL command in order to see whether or not the connection will use authentication.
When performing the lookups MDaemon will attempt to acquire all of the MX and A record IP addresses for the given domain. The purpose of the Reverse Lookup process is therefore not to exclude mail but to include as much information as possible in the log files, and to provide the means whereby the postmasters can act according to their own local policies regarding these suspicious messages. When using this option the connection can be aborted or a warning header inserted into the message if the incoming IP address does not match any PTR record.
The address passed in the MAIL command is supposed to be the reverse-path for the message, and is usually the mailbox from which the message is originating. It is very common for mail servers to identify themselves with values that do not match their IP addresses. On it you can designate IP addresses, domains, and hosts that you wish to be exempt from reverse lookups. Then the IP of the server making the connection is compared to this list in an attempt to determine whether the sender might be using a forged identity.
To that end, an option exists that makes it possible for a special header to be inserted into all messages that do not pass a reverse lookup.


In such cases, MDaemon will return a 451 error code, refuse to accept the message, and then allow the SMTP session to progress. The domain name passed by the client in this command is used by the server to populate the from portion of the Received header. The content filter system can then be used to determine the fate of messages containing the header. However, should you wish to return a 501 error code, close the socket connection, or do both, other switches are provided for those purposes.
It is likely that using this option could result in your server refusing some legitimate messages.



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