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Momentum contains a fully loaded Sieve compiler and execution engine. The sieve module provides a mechanism for you to specify Sieve scripts that should run at different phases of an SMTP transaction.


In Momentum version 3.x, Sieve continues to be supported but scripting via Lua is preferred for the following reasons:

  • Sieve has no concept of looping or iterators

  • Simple comparative logic in Sieve is awkward to author

  • Unlike Sieve, new modules do not need explicit C development to enable Lua capabilities


You cannot use Sieve with multiple event loops. If you include the Sieve module in your configuration file, Momentum will not start up and a warning will be written to the panic log. If you are upgrading to a multiple event loop configuration of Momentum, be sure to remove the Sieve module from your configuration file.

Sieve++ was developed by Message Systems specifically for Momentum. It provides you with a powerful policy management engine for both inbound and outbound mail.

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