Today we are announcing the latest release of Stalwart Mail Server: version 0.3.6. This update includes multiple enhancements to the Sieve filtering language, including the ability to evaluate arithmetical and logical expressions, and fetch data from SQL or LDAP databases to Sieve variables.
Sieve (RFC5228) is a scripting language for filtering email messages at or around the time of final delivery. It is suitable for running on a mail server where users may not be allowed to execute arbitrary programs as it has no user-controlled loops or the ability to run external programs. Sieve is a data-driven programming language, similar to earlier email filtering languages such as procmail and maildrop, and earlier line-oriented languages such as sed and AWK: it specifies conditions to match and actions to take on matching.
Sieve is a language that can be used to create filters for electronic mail. It is not tied to any particular operating system or mail architecture. It requires the use of RFC 822-compliant messages, but otherwise should generalize to other systems that meet these criteria.