18.11 Sieve Filtering Overview

A Sieve filter consists of one or more conditional actions to apply to a mail message depending upon a string found in the message header. As an administrator, you can create channel-level filters and MTA-wide filters to prevent delivery of unwanted mail. Users can create per-user filters for their own mailboxes using Messenger Express. Specific instructions for this are described in the Messenger Express on-line help.

The server applies filters in the following priority:

1. User-level filters

   If a personal mailbox filter explicitly accepts or rejects a message, then filter processing for that message finishes. But if the recipient user had no mailbox filter—or if the user's mailbox filter did not explicitly apply to the message in question—Messaging Server next applies the channel-level filter. Per-user filters are set

2. Channel-level filter

   If the channel-level filter explicitly accepts or rejects a message, then filter processing for that message finishes. Otherwise, Messaging Server next applies the MTA-wide filter, if there is one.

3. MTA-wide filter

By default, each user has no mailbox filter. When a user uses the Messenger Express interface to create one or more filters, then their filters are stored in the Directory and retrieved by the MTA during the directory synchronization process.