Individual users may use personal PMDF mailbox filters to prevent delivery of unwanted mail messages to their mailboxes. Or the PMDF manager may create channel level filters or a system wide filter.
Through a web-based interface, users construct and manage the screening rules applied by their personal mailbox filters, or the PMDF manager constructs and manages the screening rules for channel level filters or a system wide filter. System managers may customize this web interface as described in Section 16.2.6 . Personal mailbox filters are supported for use with the l (lowercase "L"), msgstore, and popstore channels. Channel level filters are supported for all channels.
Each mailbox filter contains six distinct filters: three to identify messages to always keep, the "Keep filters"; three to identify messages to always discard, the "Discard filters". The Keep and Discard filters operate on envelope and header source addresses, header destination addresses, and phrases or words appearing in the Subject: header line. The six filters are thus known by the names Keep From, Keep To, Keep Phrases, Discard From, Discard To, and Discard Phrases.
Users' personal mailbox filters are applied first. If a personal mailbox filter explicitly accepts or rejects a message, then filter processing for that message copy 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---PMDF next applies the channel level filter. If the channel level filter explicitly accepts or rejects a message, then filter processing for that message finishes. Otherwise, PMDF next applies the system filter file, if there is one.
By default, each user has no mailbox filter. When a user uses the
web-based interface, and mailbox filtering is enabled for the channel
which delivers mail to their mailbox, a mailbox filter is created for
them. Each mailbox filter is stored in a disk file, the location of
which is controlled with the filter channel keyword as
described in Section 16.2.1 .
Channel filters are not present by default. If channel level filtering
is enabled for a channel, then the PMDF manager may create a channel
level filter using the web-based interface, by authenticating as the
"address" @channel-host-name where
channel-host-name is the official host name of
the channel in question, and providing the password for the PMDF server
account.
The PMDF manager may create a system system level filter using the
web-based interface by authenticating as the "address"
@---that is, specifying the single character
@ as the "address"---and providing the password
for the PMDF server account.