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Re: "spoofed" email messages coming from recepient

2009-01-30 18:24:17
At 12:10 2009-01-30 -0800, Alex Rodriguez wrote:

I am a junior Linux admin with very limited experience with procmail.

Problem:

I need to have procmail dump email messages which have the same address on both sender and receiver field on the email envelope.

If it's envelope data, you should specify what headers your MTA is adding to the message such that programs such as Procmail can see the envelope data. This isn't inherently part of the headers.

Also, you may be better off setting up a filter in your MTA to reject these at SMTP delivery time - thus advising legitimate senders (perhaps your users) that the message is being rejected. Accepting and THEN bouncing the message is problematic.

Consider also whether you want the rule to apply only to addresses at your domain(s), or to ANY address pair - it isn't wholly uncommon for people to address a group of recipients as BCC and themselves as the TO:. This wouldn't meet the criteria of an ENVELOPE TO: and FROM: match unless of course that person was your customer (and is receiving the individual copy addressed to themselves), but if you're using non-envelope - plain From: and To: headers - then such messages will match.

If the emails you're trying to block are spoofing your own domain, you should consider setting up your MTA to require SMTP authentication. Local (shell) users would have no problems sending, and any users mailing into your SMTP would need to authenticate in order to do so. This protects your own server from being hijacked to send mail out to other sites as if they came from your users.

---
 Sean B. Straw / Professional Software Engineering

 Procmail disclaimer: <http://www.professional.org/procmail/disclaimer.html>
 Please DO NOT carbon me on list replies.  I'll get my copy from the list.

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