SQLgrey is a greylisting policy for Postfix that includes automated whitelisting and an SQL database for storage.
With SQLgrey, users can choose from three different grey-listing algorithms and utilize file-based IP and FQDN whitelists. The software also supports fetching up-to-date whitelists from a repository and sending notifications to the admin when the database is unavailable. Additionally, SQLgrey's auto-whitelists now understand SRS (SPF-aware mail forwarding), and the software provides support for IPv6 and OPTIN / OPTOUT. The fine log controls and activity reports are also great features that allow for better monitoring of email traffic.
SQLgrey excels at maintaining reliable operation in case of database crashes. Grey-listing is automatically switched off, and the software can reopen database connections on SIGUSR1. Users must meet specific requirements, including Perl, DBI, Net::Server::Multiplex (version 0.87 or higher), and either SQLite, MySQL, or PostgreSQL (with the latter being recommended).
The stable version 1.6.8 comes with crash on syslog death bugfixes and database handling fixes (deactivated InactiveDestroy unless needed) and can also reopen database connections on SIGUSR1. The developmental version 1.7.6 also offers similar database handling fixes that help solve memory leaks.
Overall, SQLgrey is an excellent software choice for those looking to reduce email spam and want a reliable greylisting policy service with advanced features that come with an SQL database backend.
Version 1.6.8 / 1.7.6: N/A