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diff --git a/US_PATENT_6321267 b/US_PATENT_6321267 new file mode 100644 index 0000000..6d86763 --- /dev/null +++ b/US_PATENT_6321267 @@ -0,0 +1,129 @@ +[The patent discussed in this document expired in 2019, without a +request for extension. The owner of that patent can no longer sue for +infringement. However, other patents may make similar claims. The text +below may serve as an example for dealing with them.] + +1. Disclaimer: This text is not an authoritative statement. If +you are concerned about the implications of US patent 6,321,267, +then you should give this text to your own lawyer and get their +advice. + +1.1 Postfix is an MTA that aims to be an alternative to the widely + used Sendmail MTA. Postfix is available as open source code + from http://www.postfix.org/. One of the features implemented + by Postfix is called "sender address verification". + +1.2 US patent 6,321,267 (reference 4.1) describes a number of means + to stop junk email. One of the elements described in this + patent is called "active user testing". + +1.3 Postfix "sender address verification" and US patent 6,321,267 + "active user testing" are implemented by connecting to an MTA + that is responsible for the sender address. Specifically, both + use the SMTP RCPT command, and both infer the validity of the + address from the MTA's response. Reference 4.3 defines SMTP. + +===================================================================== + +2. It is my understanding that the Postfix MTA's "sender address +verification" does not infringe on US patent 6,321,267 for the +following reasons: + +2.1 There is prior art for US patent 6,321,267 "active user testing" + within the context of the Sendmail MTA. See item (3.1) below. + +2.2 US patent 6,321,267 covers "active user testing" only in + combination with functions that the Postfix MTA does not + implement. See items (3.2) through (3.5) below. + +===================================================================== + +3. Discussion of specific details of US patent 6,321,267, and their +relevance with respect to the Postfix MTA. + +3.1 Prior art. The "active user testing" method is described in + the paper "Selectively Rejecting SPAM Using Sendmail" by Robert + Harker (reference 4.2). The paper is cited as the first + reference in US patent 6,321,267, and was presented in October + 1997. The patent was filed more than two years later, in November + 1999. The paper says: + + Bogus User Address + + A desirable criterion for rejecting mail is to filter on + bogus user address. However, testing for a bad user address + is much harder because, short of sending a message to that + user address, there is no reliable way to check the validity + of the address. A simplistic test for a bad user address + might be to connect to the sender's SMTP server and use + either the SMTP VRFY or RCPT command to check the address. + If the server does local delivery of the message then this + would work well. + + The prior art is about stopping junk mail with the Sendmail + MTA. It is my understanding that this prior art is equally + applicable to other MTAs, including the Postfix MTA (see items + 1.1 and 2.2 above). + +3.2 Combination of elements not implemented by the Postfix MTA. + Claim 1 of US patent 6,321,267 involves a combination of A) + determining whether the sending system is a dialup host, B) + determining whether the sending system is an open mail relay, + and C) active user testing. + + Postfix does not implement elements A) and B) of claim 1. + Therefore, it is my understanding that the Postfix MTA does + not infringe on US patent 6,321,267 claim 1. + +3.3 Combination of elements not implemented by the Postfix MTA. + Claim 52 of US patent 6,321,267 involves the combination of A) + a proxy filter and B) active user testing. + + Postfix is an MTA, not a proxy, and does not implement element + A) of claim 52. Therefore, it is my understanding that the + Postfix MTA does not infringe on US patent 6,321,267 claim 52. + + US patent 6,321,267 makes a clear distinction between proxies + and MTAs. + + Figure 13 in US patent 6,321,267 shows how a proxy interacts + with a sending system and a local MTA. In the case of (sending + system, proxy, local MTA), the proxy assumes no responsibility + for delivery of the email message. The responsibility remains + with the sending system or passes directly to the local MTA. + + Figure 4 in US patent 6,321,267 shows how a sending system + interacts with an intermediate MTA. In the case of (sending + system, intermediate MTA, local MTA), the intermediate MTA + assumes full responsibility for delivery of the email message. + + Figure 2 in US patent 6,321,267 shows how a sending system + interacts with a local MTA. In the case of (sending system, + local MTA), the local MTA assumes full responsibility for + delivery of the email message. + +3.4 The other independent claims in US patent 6,321,267 involve + elements that the Postfix MTA does not implement, and do not + involve sender address verification. Therefore, it is my + understanding that the Postfix MTA does not infringe on these + claims in US patent 6,321,267. + +3.5 All dependent claims in US patent 6,321,267 depend on claims + that involve elements that the Postfix MTA does not implement. + Therefore, it is my understanding that the Postfix MTA does + not infringe on these claims in US patent 6,321,267. + +4.References: + +4.1 Albert L. Donaldson, "Method and apparatus for filtering junk + email", US patent 6,321,267. Filing date: November 23, 1999. + http://www.uspto.gov/ + +4.2 Robert Harker, "Selectively Rejecting SPAM Using Sendmail", + Proceedings of the Eleventh Systems Administration Conference + (LISA '97), San Diego, California, Oct. 1997, pp. 205-220. + http://www.usenix.org/publications/library/proceedings/lisa97/ + full_papers/22.harker/22.pdf + +4.3 Jonathan B. Postel, "Simple Mail Transfer Protocol", August + 1982. http://www.ietf.org/rfc.html |