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Man Pages


Manual Reference Pages  -  ASSP (8)

NAME

assp - Anti-Spam SMTP Proxy

CONTENTS

Synopsis
Description
Files

SYNOPSIS

assp [ base_dir [ admin_port ] ]

%%RC_SCRIPT%% start|stop|restart|status

DESCRIPTION

Anti-Spam SMTP Proxy is a spam filter that sits on port 25 in front of your regular SMTP server (exim(8), postfix(8), qmail(8), sendmail(8), etc).

ASSP relays the SMTP dialog between an incoming client and your SMTP server, intercepting the dialog as needed. ASSP performs a number of configurable spam checks and on detecting a spam message provides an immediate 5xx SMTP error code back to the client. Non-spam messages are passed to your regular SMTP server for further processing and delivery. Spam messages can be blocked from delivery or subject-tagged and delivered.

ASSP offers:

- a whitelist of known good senders
- Bayesian checks on message headers and contents
- local user validation using RFC822 checks, flat lists or LDAP lookup
- relay denial
- HELO checking
- SPF (Sender Policy Framework) checking
- DNSBL (DNS Block List) checking using many block list services
- delaying of messages from unknown senders
- Virus detection

ASSP is entirely administrator-managed and is almost totally transparent to users. In particular, users do not need to manage procmail(1) spam filters or challenge-response systems of their own.

The base_dir argument gives the name of ASSP’s working directory. If omitted it defaults to the current directory.

ASSP is configured using a web interface. The admin_port argument gives the network port for accessing ASSP’s configuration menu. It defaults to 55555. To access the configuration menu, start ASSP and then point your browser at http://localhost:55555. The default admin password is nospam4me.

Initial setup of ASSP involves several steps:
1. Review ASSP’s configuration options and adjust as necessary. Be sure to change the admin password. By default ASSP’s filters are all set to Test Mode which means all messages will be delivered to their recipients. Leave everything in Test Mode for now.
2. Decide on which network port(s) ASSP will listen and on which your normal SMTP server will listen. Typically, ASSP will listen on port 25 and your SMTP server will be moved to something like port 125 or 587.
3. Reconfigure your SMTP server to its new port.
4. Reconfigure ASSP to port 25 and restart ASSP. Since ASSP is in Test Mode, all messages will be delivered to their recipients.
5. Arrange for all users’ outbound email to be processed by ASSP. This is necessary for ASSP to be able to automatically maintain its whitelist. If a user’s MUA uses SMTP to port 25, this will happen without further intervention. If an MUA invokes /usr/sbin/sendmail and you’re using the default sendmail(8) configuration with submit queues, this will also happen without further intervention. Otherwise, you need to take whatever steps are necessary for each MUA that’s being used.
6. Optionally, send a message containing a list of email addresses that you want to receive email from to asspwhite@yourdomain.com. Have all your users do this. This will seed ASSP’s whitelist. Messages from senders on the whitelist will never be blocked. An address can be removed from the whitelist by emailing it to asspnotwhite@yourdomain.com.
7. To set up the Bayesian word list filtering, do the following:
7a. Ensure some senders’ addresses are in the whitelist, either by sending email to them or by seeding the whilelist as described above.
7b. Allow some time (could be hours or days, depending on the volume of email you receive) for enough email to collect. Mesages from senders on the whitelist will be copied in the notspam directory. Other messages will either be passed or be copied in the spam directory based on word scores in the initial greylist.
7c. Periodically examine the messages in ASSP’s notspam and spam directories to make sure they’re sorted correctly. Move any to the other directory as needed. If you’re unsure about a particular message, just delete it. Also, examine maillog.txt for information about what ASSP is doing.
7d. After about 400 messages have collected, filtering mode can be enabled. In the /var/db/assp directory, run the /usr/local/lib/assp/rebuildspamdb.pl script to create the spam database from the logged messages. This is the part where the Bayesian filter ‘‘learns’’ about the words in your spam and notspam collections.
7e. Uncheck the appropriate Test Mode box in ASSP’s configuration menu to enable message blocking.
7f. It is recommended that the UseSubjectsAsMaillogNames configuration option is eventually unchecked and that the script /usr/local/lib/assp/move2num.pl is run in the /var/db/assp directory. This causes messages to be stored with numeric filenames, and overwritten after some time. The benefits of this are that the size of the stored messages will be limited and that older messages are removed from the collection. This keeps the Bayesian word list current. This need not be done immediately; you can do this once you no longer feel the need to examine the spam messages in detail.
8. ASSP’s other filtering options (local user validation, RFC822 conformance, client HELO validation, SPF validation, the Delay List, the use of DNSBLs and the ClamAV virus checker) can be enabled by examining and adjusting their configuration options as needed and then unchecking the appropriate Test Mode boxes.
Once ASSP is live, users should forward a copy of any spam message that still gets through to asspspam@yourdomain.com in order to add it to ASSP’s spam database. Any non-spam that was mis-classified as spam can be copied to asspnotspam@yourdomain.com.

The rebuildspamdb.pl script needs to be re-run periodically to update the spam database from the latest logged messages. There is a periodic(8) script that will do this overnight.

For full details of using ASSP, see the ASSP website and documentation.

STARTING ASSP AT BOOT TIME

The %%RC_SCRIPT%% script is run automatically at system boot time. Several variables can be set in /etc/rc.conf to control the behavior.
assp_enable set to YES to start ASSP at boot time
assp_flags passed to the ASSP client, default is assp_flags= /var/db/assp
assp_logexpire used by nightly script to expire logs, default is assp_logexpire= 45 days

FILES

/var/db/assp location of ASSP config file, log file and spam databases
/var/db/assp/notspam copies of non-spam messages received
/var/db/assp/spam copies of spam messages received
/var/db/assp/errors/{notspam,spam} messages forwarded to asspnotspam@ and asspspam@ addresses
/var/db/assp/maillog.txt ASSP’s log file
/usr/local/lib/assp/freshclam.sh script to update virus definitions
/usr/local/lib/assp/move2num.pl script to rename stored messages to numeric filenames
/usr/local/lib/assp/rebuildspamdb.pl script to update spam database
/usr/local/etc/periodic/daily/510.assp nightly script to invoke rebuildspamdb.pl and freshclam.sh.

SEE ALSO

procmail(1), assplog(8), exim(8), postfix(8), qmail(8), sendmail(8), /usr/local/share/doc/assp/ASSP Documentation.htm
http://assp.sourceforge.net/
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ASSP (8) May 16, 2005

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