Yahoo and their mail filters..

Eric Esslinger eesslinger at
Wed Feb 25 14:47:36 UTC 2009

We pretty constantly are deferred on yahoo, and at one point had all 
outbound mail for yahoo logged at the sender/recipient/subject/size 
level to get an idea what was up.

In an experiment, I found that after being 'clean' (not being deferred) 
for close to a week, simply sending myself 1 single email, then hitting 
spam in the yahoo box was enough to get us being blocked for another 24 

I would sign up for a FBL if they had one; I find the others I have very 
valuable (though about 90% of what I get back is 'spam rather than 
delete' ).
Ray Corbin wrote:
> Funny we were just having similar conversation on :) . Suresh is right about the feedback loops (you also should subscribe to comcasts/hotmails/trend micro's ( If you don't have an external gateway that makes doing reports easy then they are a good way to find out when spam problems arise, such as the pesky Nigerian spammers who constantly find new ways to thwart all anti-fraud checks prior to creating the accounts. One thing that I did, when being an email admin for a very large shared hosting company, was when I ran reports of emails going to I took the top 10 or so recipients and figured out who had the forwarders setup to send to them. I talked to the customer and even gave them alternative solutions (such as giving them 6months free for Postini inbound anti-spam service for that forward account). The worst ones were those who had catchalls setup to forward to their spam at account, those simply got notified that it was removed. 
> -r
> -----Original Message-----
> From: Suresh Ramasubramanian [mailto:ops.lists at] 
> Sent: Wednesday, February 25, 2009 6:42 AM
> To: Niall Donegan
> Cc: nanog at
> Subject: Re: Yahoo and their mail filters..
> On Wed, Feb 25, 2009 at 5:02 PM, Niall Donegan <niall at> wrote:
>> Another interesting side effect of that is email forwarder accounts.
>> Take a user who gets a domain on our shared hosting setup and forwards
>> the email for certain users to a Yahoo account. If those mails are
>> marked as spam, it seems to be our server that gets blacklisted rather
>> than the originating server.
> No surprise. Guess whose IP is the one handing off to yahoo?
> If you have forwarding users -
> * Spam filter them to reject spam rather than simply tag and forward it.
> * Isolate your forwarding traffic through a single IP,  Let ISPs know.
>> Feedback loops often aren't that useful either. We're on the AOL Scomp
>> feedback loop, and we've often got fairly personal email sent to our
>> abuse desk because the users simply press spam rather than delete.
> You have a far smaller userbase, and a userbase you know. For us, with
> random nigerians and other spammers signing up / trying to sign up all
> the time, FBLs are invaluable as a realtime notification of spam
> issues.
> And as I said random misdirected spam reports wont trigger a block as
> much as your leaking forwarded spam.  Or your getting a hacked cgi/php
> or a spammer installed direct to mx spamware.  [so if you are cpanel -
> smtp tweak/csf firewall and mod_security for apache should be default
> on your install if you havent already done so]
> -srs

Eric Esslinger
Information Services Manager
Fayetteville Public Utilities
Fayetteville, TN 37334
Phone: 931-433-1522x165   Fax: 931-433-0646
eesslinger at

More information about the NANOG mailing list