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Sendmail Validating MAIL FROM

Discussion in 'Site & Server Administration' started by digitalpoint, Apr 19, 2004.

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  1. #1
    There *must* be something like this out there, and would much rather download and install it rather than build it from scratch...

    I get well over 2,000 spams per day, so this would cut out the vast majority of them I think...

    When a SMTP session is started from a remote machine, MAIL FROM and RCPT TO is sent before the email itself.

    So I'm thinking the instant you get MAIL FROM (which is the the email address of the sender), have the receiving server initiate a SMTP session to the authoritative mail server for that email address and validate it's a real email with the RCPT TO command. If it's not a valid address, simply drop the connection from the machine trying to send you email.

    I suppose I could also do it at the MDA level with procmail or something to just send the emails to /dev/null or bounce them back if they fail my test.

    I'm pretty sure that would cut out the vast majority of the spam if I could find something like that... anyone know of such a beast?

    - Shawn
     
    digitalpoint, Apr 19, 2004 IP
  2. SEO Bob

    SEO Bob Guest

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    #2
    Hey Shawn,

    I've never heard of such a beast, but your idea is a great one. Such a product would be a great asset to everyone. To play devil's advocate though, I thought of a couple questions:

    Would the module (i'm assuming it would be a module for current MTAs) require a the server to be running a matching module?

    How do you think this would affect network traffic and would it cause excessive network congestion? (given the tradeoff from decreased spam to a couple verification packets i wouldn't be too worried about this)

    I've forwarded your post to an ex-prof of mine who's sort of my personal Linux guru. I'll let you kinow what he says.
     
    SEO Bob, Apr 20, 2004 IP
  3. digitalpoint

    digitalpoint Overlord of no one Staff

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    #3
    I actually wrote a script yesterday validates the email passed to it against the authoritative mail server.

    It's much easier to incorporate it into the MDA level (via procmail) than into the MTA (sendmail in my case), so that's probably what I'll end up doing.

    - Shawn
     
    digitalpoint, Apr 20, 2004 IP
  4. SEO Bob

    SEO Bob Guest

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    #4
    Hey Shawn,

    I was talking to the ex-prof of mine, and he said the following:

    I was planning on just posting an excerpt of this, but found it to be pretty interesting, and posted the whole thing.
     
    SEO Bob, Apr 20, 2004 IP
  5. digitalpoint

    digitalpoint Overlord of no one Staff

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    #5
    Yeah... I agree that ideally it should be done at the MTA level but have not found a plug-in that will do it (without recompiling sendmail, which I don't want to do). So for now, at the MDA level is fine. My primary goal is not saving bandwidth, rather me simply not receiving the email.

    - Shawn
     
    digitalpoint, Apr 20, 2004 IP
  6. SEO Bob

    SEO Bob Guest

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    #6
    It's really too bad that we're the only two posting on this topic. Personally, I find it to be really interesting.

    What about a solution similar to the implementation of ORBD. I'm not saying a common database, that would just be silly, more about WHEN the ORBD database is loaded, and get in there.

    Like I said, I don't know where that hapens in the sendmail cycle, or if this will help at all, but now i'm just babbling on, so I'll stop.
     
    SEO Bob, Apr 20, 2004 IP
  7. hulkster

    hulkster Peon

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    #7
    It's been a while since I've futzed with sendmail stuff (yes, many years ago I even used to tweek raw sendmail.cf's - give me a root canal instead please! ;-), but I remember a few years ago Eric Allman at an evening Usenix function talking about some new features called "Milters" that were going to be plug-ins at the MTA level to deal with stuff like this; that is, of course, where it should be handled.

    I haven't really followed it for a while, and I'm guessing Shawn has looked into this (although he said he didn't want to re-compile sendmail, and in the foggy recesses of my mind, I seem to remember that was neccessary - i.e. not just a .mc -> .cf -> HUP sendmail change), so maybe not adding much to the discussion.

    spam is one royal, royal pain - I wish I had never put my Email address on www.komar.org years ago (I took it down a while back replaced by a CGI script), but it just lives on - heck, I've even though about "throwing away" my Email address, but I like it! ;-)

    alek

    P.S. Shawn: Your approach assumes, of course, that the reply-address will ALWAYS be valid for "legit" Email - I can imagine auto-responders or whatever that are misconfigured generating a "noreply@" Email address that they fail to actually accept Email for (before presumably dumping it on the floor anyway). So while this would be "their fault", you might not get a valid message.

    I do agree this is the <1% of Emails that would fail your test - vast, vast majority would be spam with no legit return address.
     
    hulkster, Apr 20, 2004 IP
  8. SEO Bob

    SEO Bob Guest

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    #8
    Alek, you bring up a good point with the auto-responders. I had briefly considered that issue but was mostly thinking of submit forms on my sites. Of course problems with those are easy to fix since you control the site anyways. One way that you could get around that would be by interrogating the email as it's sent - from my experience the fake addresses bounce when replied to.

    Or we could just drag every spammer out into the street and throw one stone at him for every email he's ever sent. (perhaps it's unfair to assume spammers are all men, but let's face it... that hot chick that's asking for our website in ICQ is really a guy)
     
    SEO Bob, Apr 20, 2004 IP
  9. digitalpoint

    digitalpoint Overlord of no one Staff

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    #9
    Well ultimately what really needs to happen is a replacement for the SMTP protocol altogether so from addresses can't be spoofed. But until then...

    As far as auto responders and the like, if they have no legit address for me to contact them at, it really can't be all that important I'm thinking. As it is now, I loose lots of legit email because there is so much spam. It's impossible to look closely at every single email. So in reality, I think I would get more legit email...

    Anyway, I'm going to try it out on a secondary account I have for awhile (one that gets nothing BUT spam... it's the email I register domains with, and that's it's only purpose. I like to keep it around when I want to test spam filters, because 100% of the 250 or so per day I get there are spam).

    - Shawn
     
    digitalpoint, Apr 20, 2004 IP
  10. hulkster

    hulkster Peon

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    #10
    How 'bout having the Hulk drop from a two story houseon top of 'em for every spam Email they have sent out! ;-)

    Spammers have seriousely degraded the usefullness of Email,
    alek

    P.S. Shawn: bummer on the domain registrations being a harvesting pit for the spammers - kinda defeats the whole purpose of whois. I agree that SMTP needs a replacement and as I'm sure you are aware, there are various proposals out there, but it's going to be a while.
     
    hulkster, Apr 20, 2004 IP
  11. digitalpoint

    digitalpoint Overlord of no one Staff

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    #11
    I know... just wish an SMTP replacement would hurry up. It will be painful at first I'm sure but worth it in the end.

    - Shawn
     
    digitalpoint, Apr 20, 2004 IP
  12. hulkster

    hulkster Peon

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    #12
    AMEN!!!!
    alek

    P.S. Since anti-spam filters are basically a requirement now, it is unavoidable that they incorrectly classify some "good" Email, so there is now a fair amount of doubt if your "legit" messages get to people ... or vice-verse.
     
    hulkster, Apr 20, 2004 IP
  13. hulkster

    hulkster Peon

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    #13
    FYI FWIW: Looks like Postfix2.1 was just released - Wietse had done some nifty stuff over the years (with a real focus on security), and while I don't have any direct experience with this, I bet it's pretty decent.

    As you probably allready know, qmail is another option besides sendmail, but there seems to be a real love/hate relationship with qmail and the author, so your mileage may vary.

    alek
     
    hulkster, Apr 23, 2004 IP
  14. vaishalichitale

    vaishalichitale Guest

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    #14
    hello, I am new user just saw your details while searching on google.
    I am also facing same problem. have you got any solution for this.
    Please mail me on vaishali.chitale@kbl.co.in
     
    vaishalichitale, Jun 20, 2006 IP
  15. netvisao

    netvisao Peon

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    #15
    Since anti-spam filters are basically a requirement now, it is unavoidable that they incorrectly classify some "good" Email, so there is now a fair amount of doubt if your "legit" messages get to people ... or vice-verse.
     
    netvisao, Sep 30, 2009 IP