[TowerTalk] Bounces

[Al Kozakiewicz]

It depends on whether and how the receiving mail server is configured to deal with incoming email.  Note that I'm assuming the problem is people with (e.g.) yahoo.com addresses receiving bounce messages when they send to contesting.com.

In the case of Yahoo.com, their servers know with certainty who is allowed to send mail on behalf of yahoo.com.  Contesting.com is definitely not on the list of Yahoo authorized senders, so it rejects the delivery attempt and contesting.com, in turn, bounces the email back to the sender, The issue I see is with yahoo, or ANY email server, is what to do if it receives an email from a server and it cannot determine whether that server is authorized to send mail on behalf of the domain in the FROM: clause.

Spf is a good example of how this scheme is supposed to work and also illustrates the rather mediocre results (filtering out spam) you can expect without universal adoption. For the uninitiated: DNS (domain name service) is a directory program that translates names to IP addresses. For example, www.hourglass.com (picking a simple example - sites like Yahoo are more complicated because they will have several servers that can service requests for www.yahoo.com) translates to 209.157.71.217.  How the directory works for your browser is that your computer queries a DNS server specified by your ISP.  That DNS server probably says "I don't know about hourglass.com, let me find out by asking the DNS server that hosts that domain."  Eventually it finds a server that is "authoritative" for hourglass.com and asks what the IP address s for www and that DNS server returns 209.157.71.217. At which point, your browser connects to 209.157.71.217 to read the webpage.

In order to send mail, your mail server looks for a special directory entry called an mx record.  The mx record tells the server asking what the IP address is of a mail server that will process incoming mail for hourglass.com.

To help beat spammers, spf was introduced a number of years ago.  This is a record in the domain DNS server that lists all the IP addresses are allowed to SEND email claiming to come from, say, hourglass.com. So if you want to reduce spam, you can query the hourglass.com DNS server and find out if the email advertising cheap Viagra actually originated from one of the servers listed in the spf record.  If not, the email can be safely rejected.

The problems arise when a domain DNS has NO spf record at all. At that point, the receiver has no idea whether the email originates from a legitimate source.  The safe thing to do at that point is to just let the email pass through; otherwise the false positives would cause too much email to be rejected as spf has not been universally adopted.

Sorry for the long-winded explanation...

Al
AB2ZY

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of john at kk9a.com
Sent: Monday, April 14, 2014 8:21 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Bounces

Until I purchased my own domain, I used the arrl.net forwarder and sent emails as kk9a at arrl.net.  It is easy to do with Outlook, Outlook Express, gmail and many other programs. I am not sure that using a forwarder will solve all of the bounce problems.

John KK9A


To:	 towertalk reflector <TowerTalk at contesting.com>
Subject:	 Re: [TowerTalk] Bounces
From:	 Mike Reublin NF4L <nf4l at comcast.net>
Date:	 Mon, 14 Apr 2014 16:24:37 -0400
List-post:	 <towertalk at contesting.com">mailto:towertalk at contesting.com>
Thanks for the info Gary. I'm a Comcast user, and I got un-subscribed.

I don't think it's possible to use a remailer such as ARRL or pobox because the "FROM" header is still going to be your real email provider. If you know how to do it, please post instructions.

73, Mike NF4L

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