Date: Sun, 22 Apr 2001 01:30:02 -0700 (PDT) From: "Ted Mittelstaedt" <tedm@toybox.placo.com> To: freebsd-advocacy@freebsd.org Subject: Re: misc/26744: Unable to send mail to FreeBSD.org from home and from work Message-ID: <200104220830.f3M8U2076525@freefall.freebsd.org>
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The following reply was made to PR misc/26744; it has been noted by GNATS. From: "Ted Mittelstaedt" <tedm@toybox.placo.com> To: <freebsd-gnats-submit@FreeBSD.org>, <riccardo@torrini.org> Cc: Subject: Re: misc/26744: Unable to send mail to FreeBSD.org from home and from work Date: Sun, 22 Apr 2001 01:25:09 -0700 Here's another question for the FAQ: HELP! I can't send e-mail from my newly installed FreeBSD system (AKA I can't send mail to freebsd.org) [Preamble] Note that this is NOT the RECIPIENT'S problem, this is a SENDER'S problem - ie: YOU. A cardinal rule on the Internet is that any mailserver is permitted to _not_ accept any mail for any reason whatsover. YOU do NOT have a right to TRANSMIT mail to anyone you choose. However, the RECIPIENT _always_ has the right to REJECT any mail they want to. Now that we got that straight, here's how YOU can fix YOUR server. [explanation] Unfortunately, the increased amount of spamming done on the Internet has forced most administrators running mailservers to take action to block spam, or mail messages that have a high probability of being spam. As a result of this, today most mailservers require ONE of the following at minimum to accept an incoming E-mail message: 1) The mail message must be originating from an IP number that is an "allowed set" of IP numbers. 2) The mail message must be originating from an IP number that is both forward and reverse resolvable in the DNS, and in addition those resolutions must be symmectrical. For example, a user has a FreeBSD system that is named "freebsd.example.org" and that is dialed into a dialup ISP using PPP. The FreeBSD system has an IP number assigned by the ISP of 155.4.3.5. For any arbitrary mailserver on the Internet to accept mail from the user's FreeBSD system, any Internet user MUST be able to issue the command "nslookup 155.4.3.5" and get the name "freebsd.example.org" and must ALSO be able to issue the command "nslookup freebsd.example.org" and get a response of the IP number 155.4.3.5 If they cannot do this, or if the first nslookup gets a name like "dialup-pool-5.myisp.example.org" and the second nslookup gets a response like "host not found", then you while you will be able to SEND mail, very few mailservers on the Internet will permit RECEPTION of your mail message. [answer] To get around this, assuming that your ISP's master mailserver is named "mail-myisp.example.org" what you need to do is modify the file /etc/mail/sendmail.cf and find the line: # "Smart" relay host (may be null) DS and modify the DS line as such: DSmail-myisp.example.org then force sendmail to reread it's config file with the command: kill -HUP `head -1 /etc/mail/sendmail.pid` This makes your mailserver spool all outgoing e-mail through your ISP's mailserver, which presumably will accept mail from you by use of rule #1 detailed above. (allowed IP numbers) If your ISP's mailserver is screwed for some reason, then find what is known as a "promiscious open relay" mailserver on the Internet and use that. (it's a poor substitute, since those systems generally get black-holed very quickly by ORBS and MAPS) Or, better yet, complain to your ISP, this is what your paying them for. Note that the FreeBSD mailserver that the freebsd-questions mailing list is running on is one of those Internet mailservers that follows the above rules. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-advocacy" in the body of the message
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