# Pigeonhole Sieve Interpreter¶

The Pigeonhole project provides Sieve support as a plugin for Dovecot’s Local Delivery Agent (LDA) and also for its LMTP service. The plugin implements a Sieve interpreter, which filters incoming messages using a script specified in the Sieve language (RFC 5228). The Sieve script is provided by the user and, using that Sieve script, the user can customize how incoming messages are handled. Messages can be delivered to specific folders, forwarded, rejected, discarded, etc.

## Supported Features¶

Sieve language has various extensions. You can find more information about the extensions from the Sieve Mail Filtering Language Charter or the Sieve.info wiki page.

Note

Sieve doesn’t support running external programs.

The Pigeonhole Sieve interpreter recognizes the following Sieve extensions:

Not all extensions are enabled by default, as shown in the table above. Deprecated extensions, extensions that add the ability to change messages, extensions that require explicit configuration and extensions that are still under development are not enabled without explicit configuration. This means that the sieve_extensions or sieve_global_extensions settings need to be adjusted accordingly. Also, for plugins it is not enough to add the plugin name to the sieve_plugins setting; the extensions introduced by the plugin also need to be enabled explicitly.