SpamAssassin is a rule-based mail filter that identifies spam. It uses a
wide range of heuristic tests on mail headers and body text to identify
spam.
SpamAssassin filtering is configured on two levels:
- Server-level configuration is done by Plesk administrator.
- Mail directory-level configuration is done by users for specific mail
directories.
At the server level, you (as a Plesk administrator) can enable or
disable any of these two types of filters. Thus, there are four possible
situations:
- No filtering is applied:
- both filters are disabled by the Plesk administrator.
- the personal filter is disabled at the mail directory level.
- Filtering is applied at the server level only.
- Filtering is applied at the mail box level only.
- Filtering is applied at both levels.
When both filters are enabled for a specific mail name, a combined
filter is created for the corresponding mail directory. When processing
messages, SpamAssassin calculates the number of hits according to its
external rules. A message is considered to be spam if the number of hits
exceeds the established threshold, which is set to 7 by default. You can
change the threshold in Plesk. White and Black lists can be considered
special rules, which assign constant hit rates to messages conforming to
mail address patterns in these lists:
If the message source address conforms to the Black list, the message
gets +100 hits by default.
If the message source address conforms to the White list, the message
gets -100 hits by default.
Sometimes, a message matches both Black and White lists. In that case,
it has +100-100=0 hits.
If the message destination address is included in the server-wide ignore
list, then all messages to this address will go directly to the
addressed mail directory.
At the server level, you can configure SpamAssassin to mark messages
with a special string if they are recognized as containing spam. At the
mailbox level, you can make SpamAssassin delete or mark the message if
it is considered as spam.
Starting from Plesk 9.x, the maximum message size to filter is hardcoded
in the spam handler and set to 256KB. This value provides normal server
loading. Since the SpamAssassin service consists of perl modules, they
may result in a heavy server load when processing long messages.
You can obtain more information about SpamAssassin at
spamassassin.apache.org