11. Disclaimer: This text is not an authoritative statement. If 2you are concerned about the implications of US patent 6,321,267, 3then you should give this text to your own lawyer and get their 4advice. 5 61.1 Postfix is an MTA that aims to be an alternative to the widely 7 used Sendmail MTA. Postfix is available as open source code 8 from http://www.postfix.org/. One of the features implemented 9 by Postfix is called "sender address verification". 10 111.2 US patent 6,321,267 (reference 4.1) describes a number of means 12 to stop junk email. One of the elements described in this 13 patent is called "active user testing". 14 151.3 Postfix "sender address verification" and US patent 6,321,267 16 "active user testing" are implemented by connecting to an MTA 17 that is responsible for the sender address. Specifically, both 18 use the SMTP RCPT command, and both infer the validity of the 19 address from the MTA's response. Reference 4.3 defines SMTP. 20 21===================================================================== 22 232. It is my understanding that the Postfix MTA's "sender address 24verification" does not infringe on US patent 6,321,267 for the 25following reasons: 26 272.1 There is prior art for US patent 6,321,267 "active user testing" 28 within the context of the Sendmail MTA. See item (3.1) below. 29 302.2 US patent 6,321,267 covers "active user testing" only in 31 combination with functions that the Postfix MTA does not 32 implement. See items (3.2) through (3.5) below. 33 34===================================================================== 35 363. Discussion of specific details of US patent 6,321,267, and their 37relevance with respect to the Postfix MTA. 38 393.1 Prior art. The "active user testing" method is described in 40 the paper "Selectively Rejecting SPAM Using Sendmail" by Robert 41 Harker (reference 4.2). The paper is cited as the first 42 reference in US patent 6,321,267, and was presented in October 43 1997. The patent was filed more than two years later, in November 44 1999. The paper says: 45 46 Bogus User Address 47 48 A desirable criterion for rejecting mail is to filter on 49 bogus user address. However, testing for a bad user address 50 is much harder because, short of sending a message to that 51 user address, there is no reliable way to check the validity 52 of the address. A simplistic test for a bad user address 53 might be to connect to the sender's SMTP server and use 54 either the SMTP VRFY or RCPT command to check the address. 55 If the server does local delivery of the message then this 56 would work well. 57 58 The prior art is about stopping junk mail with the Sendmail 59 MTA. It is my understanding that this prior art is equally 60 applicable to other MTAs, including the Postfix MTA (see items 61 1.1 and 2.2 above). 62 633.2 Combination of elements not implemented by the Postfix MTA. 64 Claim 1 of US patent 6,321,267 involves a combination of A) 65 determining whether the sending system is a dialup host, B) 66 determining whether the sending system is an open mail relay, 67 and C) active user testing. 68 69 Postfix does not implement elements A) and B) of claim 1. 70 Therefore, it is my understanding that the Postfix MTA does 71 not infringe on US patent 6,321,267 claim 1. 72 733.3 Combination of elements not implemented by the Postfix MTA. 74 Claim 52 of US patent 6,321,267 involves the combination of A) 75 a proxy filter and B) active user testing. 76 77 Postfix is an MTA, not a proxy, and does not implement element 78 A) of claim 52. Therefore, it is my understanding that the 79 Postfix MTA does not infringe on US patent 6,321,267 claim 52. 80 81 US patent 6,321,267 makes a clear distinction between proxies 82 and MTAs. 83 84 Figure 13 in US patent 6,321,267 shows how a proxy interacts 85 with a sending system and a local MTA. In the case of (sending 86 system, proxy, local MTA), the proxy assumes no responsibility 87 for delivery of the email message. The responsibility remains 88 with the sending system or passes directly to the local MTA. 89 90 Figure 4 in US patent 6,321,267 shows how a sending system 91 interacts with an intermediate MTA. In the case of (sending 92 system, intermediate MTA, local MTA), the intermediate MTA 93 assumes full responsibility for delivery of the email message. 94 95 Figure 2 in US patent 6,321,267 shows how a sending system 96 interacts with a local MTA. In the case of (sending system, 97 local MTA), the local MTA assumes full responsibility for 98 delivery of the email message. 99 1003.4 The other independent claims in US patent 6,321,267 involve 101 elements that the Postfix MTA does not implement, and do not 102 involve sender address verification. Therefore, it is my 103 understanding that the Postfix MTA does not infringe on these 104 claims in US patent 6,321,267. 105 1063.5 All dependent claims in US patent 6,321,267 depend on claims 107 that involve elements that the Postfix MTA does not implement. 108 Therefore, it is my understanding that the Postfix MTA does 109 not infringe on these claims in US patent 6,321,267. 110 1114.References: 112 1134.1 Albert L. Donaldson, "Method and apparatus for filtering junk 114 email", US patent 6,321,267. Filing date: November 23, 1999. 115 http://www.uspto.gov/ 116 1174.2 Robert Harker, "Selectively Rejecting SPAM Using Sendmail", 118 Proceedings of the Eleventh Systems Administration Conference 119 (LISA '97), San Diego, California, Oct. 1997, pp. 205-220. 120 http://www.usenix.org/publications/library/proceedings/lisa97/ 121 full_papers/22.harker/22.pdf 122 1234.3 Jonathan B. Postel, "Simple Mail Transfer Protocol", August 124 1982. http://www.ietf.org/rfc.html 125