qmail-smtpd badmailfrom-unknown addon

this patch against a vanilla qmail-1.03 adds another control file to qmail-smtpd. This control file named

    control/badmailfrom-unknown

is only consulted if the IP address of the connecting client does not have a PTR record in DNS. In that case tcpserver doesn't set TCPREMOTEHOST and qmail-smtpd sets the variable remotehost to unknown. If this is true qmail-smtpd with the diff applied does an additional check of the domain of the envelope sender against the control/badmailfrom-unknown control file. The syntax for that file is the same as for control/badmailfrom.

The benefit of this modification is that a lot of spammers use evelope sender addresses of wellknown public mail services like

hotmail.com

yahoo.com

bigfoot.com

lycos.com

...

which you obviously don't want to put in control/badmailfrom to block all traffic from this sender domains. A lot of spam with these sender domains arrives from hosts without a PTR record in DNS and I've barely seen legitimate messages coming in that way, so blocking them is IMHO a good idea.

The patch is "shielded" by the #define __mBMF_UNKNOWN at the top of qmail-smtpd.c. Undefining it disables the modification.

Within one week running qmail-smtpd with this modification we filtered out about 1200 messages a day on a system receiving about 80000 messages a day.

download:

• badmailunk.diff (3404 Bytes)
• my currently used badmailfrom-unknown (1346 Bytes / 103 domains listed)

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