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Automatically detects and blocks open mail relays

'Smtpblock' parses a *nix mail log. When new mail messages are detected, it performs DNSBL/SMTP relay tests. If the host is listed in a DNSBL or relays third-party mail, Smtpblock creates a firewall rule to block access to the localhost's SMTP port and/or creates a hash that can be referenced by sendmail's RFC-822 pattern matching feature. It keeps track of each host's test status and time when it will need to be rechecked, reducing the need to constantly check every host sending mail to the local system. Smtpblock can be run as a daemon continuously checking the mail log or as a standalone program parsing the entire log file. Hosts can be manually checked, blocked, or unblocked from the command line.



Verified by

Verified on


Verified by

Janet Casey

Verified on

22 August 2002

Leaders and contributors

David Bellizzi Maintainer

Resources and communication

AudienceResource typeURI
Bug Tracking,Developer,

Software prerequisites

Required to usesendmail
Required to useNet_Netmask
Required to useNMAP
Required to usePerl 5.002 or later


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