Articles I read today

It has been a rather busy day today, I do not have a full blog post. I did see a couple posts come across my RSS feeds. Both of them have content I want to talk about and discuss in a little more detail, as I think they touched on some very interesting issues.
Network World has an article interviewing Mark Risher from Yahoo. The article discusses Yahoo’s use of DomainKeys as part of their inbound mail filtering.
Mickey has an article about how to deal with ISPs when attempting to troubleshoot a blocking issue.
More details and commentary on both articles later this week.

Related Posts

Greylisting: that which Yahoo does not do

Over the last couple days multiple people have asserted to me that Yahoo is greylisting mail. The fact that Yahoo itself asserts it is not using greylisting as a technique to control mail seems to have no effect on the number of people who believe that Yahoo is greylisting.
Deeply held beliefs by many senders aside, Yahoo is not greylisting. Yahoo is using temporary failures (4xx) as a way to defer and control mail coming into their servers and their users.
I think much of the problem is that the definition of greylisting is not well understood by the people using the term. Greylisting generally refers to a process of refusing email with a 4xx response the first time delivery is attempted and accepting the email at the second delivery attempt. There are a number of ways to greylist, per message, per IP or per from address. The defining feature of greylisting is that the receiving MTA keeps track of the messages (IP or addresss) that it has rejected and allows the mail through the second time the mail is sent.
This technique for handling email is a direct response to some spamming software, particularly software that uses infected Windows machines to send email. The spam software will drop any email in response to a 4xx or 5xx response. Well designed software will retry any email receiving a 4xx response. By rejecting anything on the first attempt with a 4xx, the receiving ISPs can trivially block mail from spambots.
Where does this fit in with what Yahoo is doing? Yahoo is not keeping track of the mail it rejects and is not reliably allowing email through on the second attempt. There are a couple reasons why Yahoo is deferring mail.

Read More

PBL and Yahoo

A few days ago I posted about Yahoo using the Spamhaus lists. In the comments of that post there have been multiple reports of mail being bounced from Yahoo with a reason of “on the PBL” but the IP was not on the PBL.
I am happy to look into this for people. I’m sure neither Spamhaus nor Yahoo want to be incorrectly rejecting email. To do this, though, I need the rejection message from Yahoo, the IP the mail was sent from and when it happened. Feel free to email the information to laura at wordtothewise.com.

Read More

ISP Postmaster sites

A number of ISPs have email information and postmaster sites available. I found myself compiling a list of them for a client today and thought that I would put up a list here.

Read More