Panix Help System: Spam blocking

Advanced Anti-Spam Options

Users can activate a number of highly effective anti-spam options from the SquirrelMail webmail interface at mail.panix.com. These options block spam at the server. Blocked mail is bounced (returned to the apparent sender with a "delivery failure" message)

The upside of this is that you don't see the mail that was rejected. You don't have to sift through it trying to figure out whether you should bother reading it. It never counts against your quota, and our servers don't have to go through the delivery process for it. This saves a lot of resources (human and machine).

The downside of this is that you don't see the mail that was rejected; that is, there isn't any way for you to pre-test these blocks to make sure they aren't rejecting mail you want to receive.

Remember: If you use blocking, you don't have any way of seeing a list of messages addressed to you that you didn't receive. The senders of such messages should receive "bounce" mail-- notification of non-delivery-- if their providers are using established standards. Bounce messages include an explanation of why the mail couldn't be delivered. They should then address the problem with their provider.

The specific blocks that we recommend (Zen and SpamCop in particular; greylisting secondarily) are extremely reliable and do not reject mail from properly configured servers that handle mail normally-- but not all servers behave properly.

Panix turns on Zen by default; you can turn it off if you prefer. You can still use SpamAssassin to filter spam as it's delivered to you, and you can use either the webmail-based version or the version that runs from procmail.

To activate (or deactivate) any of these blocks:

Log into webmail (select SquirrelMail);
Select the Options link at the top of the page,
Select Advanced Anti-spam Options.
Check the "Enabled" box (under "Parameters") for each of the items you want applied,
Click the Submit button at the bottom of the page to set these up on the server.

Blocks currently available

Restriction	Description
ZEN	Blocks any IP address listed on the Spamhaus Zen list, which is a combination of several other lists, including the SBL, CBL, and PBL (described below). These lists are very effective in blocking spam. See www.spamhaus.org/zen/.
CBL	Tests whether the SMTP client is listed in the Composite Blocking List (CBL). The CBL uses spamtraps to find open proxies and spam-emitting zombies, with a conservative approach to listing. See http://cbl.abuseat.org/.
SBL	Tests whether the SMTP client is listed in the Spamhaus Block List (SBL). The SBL tracks verified spam sources. See www.spamhaus.org/sbl/.
PBL	Blocks any IP address listed on the Spamhaus PBL list, which identifies end user machines (such as DSL customers or cable customers) that are not legitimate mail servers. See www.spamhaus.org/pbl/.
SpamCop	Blocks IP addresses listed by the SpamCop list of sites that send spam to spamtraps or that send mail that is reported as spam by SpamCop volunteers. See www.spamcop.net/.
Graylist	Accepts mail only on the second and subsequent attempts from a given {sender,recipient,remote server}. Some spam is only tried once. WARNING: Incoming mail, especially from people who have not mailed to you before, will be delayed 15 minutes or more. See projects.puremagic.com/greylisting/.
Reject Unknown Client	(Not recommended.) This very aggressive restriction rejects mail from SMTP clients which do not have matching forward and reverse DNS. WARNING: this will bounce some legitimate mail.