Email messages in the Pegasus Mail client. |
Email address in the Yahoo! Mail Options. |
said by Rosie :
Thank you NormanS for the clarification on the AT&T domain names. I'm unclear about the "handed off" thing. Does that mean that the spam filters are applied at the AT&T MX server first such that some emails may be deleted or bounced back before they can get "handed off" to the Yahoo servers?
Based on some tests I did a while ago, the AT&T MX servers do some basic filtering by DNSBL, and similar criteria. Email will either be accepted, or rejected a this point. Rejected email results in a "bounce" generated by the sending relay client (if that relay client is a spamming 'bot, no "bounce" is generated). Accepted email is forwarded to Yahoo! Mail Delivery Agents for placement in the user's mailbox.
Are the emails that get through being filtered again at Yahoo?
Yes. The Yahoo! MDAs provide additional filtering based on the criteria established for SpamGuard. Nearly as I can tell, no "bounces" are generated at this point; rather, email is either routed to the Inbox, or the Bulk folder. This is actually a "Good Thing®" because a "bounce" generated at this point could only go to the Return_Path email address; in spam this is forged, or fake, about 99% of the time. This would result in "backscatter": Sending "bounces" to uninvolved parties.
Just an example of what you should see in this process:
Received: from 207.115.36.38 (EHLO nlpi009.prodigy.net) (207.115.36.38)
by mta148.sbc.mail.mud.yahoo.com with SMTP; Wed, 02 Apr 2008 07:53:46 -0700
X-Originating-IP: [65.55.175.211]
Received: from blu139-omc3-s11.blu139.hotmail.com (blu139-omc3-s11.blu139.hotmail.com [65.55.175.211])
by nlpi009.prodigy.net (8.13.8 inb regex/8.13.8) with ESMTP id m32Erjfb014056
for <%User_ID%@pacbell.net>; Wed, 2 Apr 2008 09:53:45 -0500
Received: from BLU110-DS2 ([65.55.162.188]) by blu139-omc3-s11.blu139.hotmail.com with Microsoft SMTPSVC(6.0.3790.3959);
Wed, 2 Apr 2008 07:53:45 -0700
Subject: [TEST] Routing of email through at&t Yahoo! HSI service
The "Received" line at the bottom of the list is reporting my client connection (Windows Live Mail) to a Windows Live Mail account.
The "Received" line in the middle is the ATTIS MX server for the 'pacbell.net' domain accepting the email from the 'live.com' SMTP relay agent. This is where the initial filtering will take place; and the "accept/reject" decision would be made.
The "Received" line at the top is the Yahoo! MDA for this 'pacbell.net' account. This is where the filtering decision for "Inbox/Bulk" will take place.
By comparison, here is a straight Yahoo! email address. These headers from a 'yahoo.com' email address added to that 'pacbell.net' account as an "Extra" email address through the Mail Options:
Received: from 65.55.175.212 (EHLO blu139-omc3-s12.blu139.hotmail.com) (65.55.175.212)
by mta462.mail.mud.yahoo.com with SMTP; Wed, 02 Apr 2008 08:35:29 -0700
Received: from BLU110-DS3 ([65.55.162.187]) by blu139-omc3-s12.blu139.hotmail.com with Microsoft SMTPSVC(6.0.3790.3959);
Wed, 2 Apr 2008 08:31:36 -0700
Subject: [TEST] Extra email address
This was picked up by the same account. You will see that this time the email goes straight to the Yahoo! server, bypassing the ATTIS server.
The screen shots show both email messages in the client folder, and the Yahoo! Mail Options screen where the extra accounts are set up.