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Re: Filter by correct addresses?

2001-01-18 12:58:02
At 11:34 2001-01-18 -0600, Dustin Ankeny wrote:
I don't know if this is common or not, but 80% of the spam that my users get
is not addressed to them.

Uhm, so is nearly 100% of list email. Please refer to THIS message as an example.

Example:
joebob(_at_)mydomain(_dot_)com receives mail for 
joebob(_at_)isp_mailservername(_dot_)com and
joebob(_at_)unrelateddomain(_dot_)com

If these are KNOWN spam target addresses, you might just add them to a blacklist file and filter against that.

Anyway I would like to separate/delete all mail that is not a "correct"
address.

You're skating on thin ice when you start deleting user email. You're better off using /etc/procmailrc to add an "X-SUSPECT:" header or similar, and tell your users that they might use that to filter out the spam. Then, start using some of the heuristics various people have posted to this list over the years.

I would like to have a file that houses all valid addresses and if the mail
is not to any of those addresses, it gets deleted.

Well, at some level, it IS to one of those addresses. Your Fetchmail process may complicate the process if you're fetching from a remote mailbox rather than having it sent over via SMTP (by issuing an ETRN command).

Has anyone else done something like this? Is this safe and is this problem common with other ISP's?

I prefer to filter my _own_ email. Beyond that, I employ RBL, DUL, RSS, ORBS, etc. at the SMTP level (along with relay checking and other spam rules in newer versions of sendmail), plus the sendmail access database to block repeat offenders.

As for other ISPs - if my ISP filtered email discarding things that seemed to be spam just because I wasn't a cleartext recipient, I'd find a new ISP.

Note that plussed addressing could complicate matters for you (user+token(_at_)domain(_dot_)com is valid per RFC, and sendmail supports it, as does procmail). While the outlook users probably aren't using it, it is something to keep in mind.

---
 Please DO NOT carbon me on list replies.  I'll get my copy from the list.

 Sean B. Straw / Professional Software Engineering
 Post Box 2395 / San Rafael, CA  94912-2395

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