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.
Stalwart IMAP includes support for ManageSieve which allows users to upload and manage their Sieve scripts. Requests received by the ManageSieve server are sent to the JMAP server using the JMAP for Sieve Scripts protocol.
ManageSieve is enabled by specifying the port number where the server will listen for incoming connections, which is configured
bind-port-sieve parameter. For example, to use the default ManageSieve port
Since the ManageSieve server is actually a ManageSieve-to-JMAP-for-Sieve proxy, all configuration of the Sieve compiler and runtime has to be done at the JMAP server. For Stalwart JMAP please refer to the Sieve configuration section.