Re: [Assp-user] New (to me) anti spam technique - SPF

[Scott H. <sc...@sc...>]

Say I'm a spammer, I have a throw away domain, I run my own DNS, I'm going to give all my machines the name of mail1-x.mydomain.com, thus getting around this idea.

In a perfect world this would work, then again in a perfect world there wouldn't be any spam either.

Good idea though.


---------- Original Message ----------------------------------
From: "Sherif Mohamed" <she...@me...>
Reply-To: ass...@li...
Date:  Fri, 19 Mar 2004 19:09:34 +0200

>I thought of an idea, it seems simple to me that probably it was thought of
>before.
>
>The idea is if any MTA recieves an email, it should check the reverse lookup
>of the sender MTA, if it mail.anydomain, mail is accepted, if it's name does
>not contain the world mail as the first name, the email is rejected.
>
>This will allow system admins of DNSs to select which email servers are
>authorized to send emails, and also ARIN and RIPE can disable reverse lookup
>for a block if they found that the a block is sending spam and authorized
>people of this block are not co-operative to stop the spammer.
>
>And it won't allow any hacked PC connected to the net to send virus and
>spams, also it does not need PK, special extra DB, list or additional s/w
>except a simple module at the MTA to reject the emails after the DNS reverse
>lookup.
>
>The thing left is that a user uses an existing real outgoing SMTP server to
>send spam, and this will be easy for the ISP admin to catch using the phone
>number or the account (or IP in case of leased lines).
>
>I see this is simple, wonder why it is not used, or maybe I am missing
>something.
>
>
>----- Original Message ----- 
>From: "John Hanna" <jh...@cp...>
>To: <ass...@li...>
>Sent: Thursday, March 18, 2004 8:09 PM
>Subject: Re: [Assp-user] New (to me) anti spam technique - SPF
>
>
>> There are a couple of these sorts of ideas in the works. AOL supports SPF,
>> Yahoo has their own idea, MSN has yet a third one.
>>
>> The simple goal of all these methods is to try to give mail servers the
>> ability to validate that a mail is from whom it claims to be from.
>> Unfortunately this is not all that helpful to stop spam for the following
>> reasons:
>>
>> 1) It is common to relay mail for another. In this case, your mail comes
>> from someone besides the sender and verification doesn't help.
>> 2) Email signing usually (a) adds overhead to the server to verify
>> signatures (and then there's always the PKI problem) and (b) weakens the
>> ability to send anonymous email. (Is that bad? Maybe not, but there is a
>> liberty issue here.)
>> 3) Postage systems make legitimate bulk email a problem.
>> 4) So what do you do if you find that a mail claims to be from someone
>> that's not allowed (by signature or server verification)? Just reject
>> everything? This doesn't solve the filter problem.
>> 5) None of these systems mean anything until a critical mass of servers
>> implement them.
>>
>> In the end, a well trained Bayesian filter is much more effective than
>these
>> SMTP level changes.
>>
>> Of these developments I'm most interested in non-monetary postage. I could
>> envision something like this:
>>
>> SMTP client connects
>> initial SMTP conversation: helo, mail from, rcpt to, DATA
>> server evaluates what's been given: connecting ip, helo, from, receipt tos
>> and calculates a likelihood of spam. If that likelihood is high enough it
>> asks for "postage" -- if it's very high it asks for a lot, little if not.
>It
>> asks for postage by delivering a 128 bit random string and the amount of
>> postage (a number between 1 and 63). The client can respond by saying,
>> "never mind" or by giving back a string which when MD5'd has 64+postage
>> number of bits in common with the random number. Postage 63 would take a
>> million years to calculate; postage 1 would take two tries (just a few
>> milliseconds) to calculate. Anyway if the server accepts the response,
>then
>> it allows the mail. Spammers pay in computer time to have spam delivered.
>>
>> We'll watch as things develop.
>>
>> John
>>
>> ----- Original Message ----- 
>> From: "Gene Cooper" <gcooper@SonoraComm.COM>
>> To: <ass...@li...>
>> Sent: Thursday, March 18, 2004 9:15 AM
>> Subject: [Assp-user] New (to me) anti spam technique - SPF
>>
>>
>> > In the latest Linux Journal, I recently read about a new anti-spam
>feature
>> > implemented via DNS called SPF.  It sounds like it would help in the war
>> on
>> > spam.
>> >
>> > http://interactive.linuxjournal.com/Magazines/LJ120/7327.html
>> > http://www.nwfusion.com/news/2004/0122aoltest.html
>> >
>> > This may not be the 'end all', but this sounds like something that might
>> be
>> > appropriate for ASSP.
>> >
>> > G
>> >
>> > ===========================
>> > Gene Cooper
>> > Sonora Communications, Inc.
>> > 5531 N. Oracle Road
>> > Tucson, AZ  85704
>> > (520) 293-8461
>> > gc...@so...
>> >
>> >
>> >
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>>
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