Tag: Technical

Check your tech

One of the things we do for just about every new client coming into WttW is have them send us an email from their bulk mail system. We then check it for technical correctness. This includes things like reviewing all the different From headers, rDNS of the connecting IP, List-Unsubscribe headers and authentication. This is […]

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PTR Records

PTR records are easy to over look and they have a significant impact on your ability to deliver mail without them.  Some ISP and mailbox providers will reject mail from IP addresses that do not have a PTR record created. PTR records are a type of DNS record that resolves an IP address to a […]

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AHBL Wildcards the Internet

AHBL (Abusive Host Blocking List) is a DNSBL (Domain Name Service Blacklist) that has been available since 2003 and is used by administrators to crowd-source spam sources, open proxies, and open relays.  By collecting the data into a single list, an email system can check this blacklist to determine if a message should be accepted […]


M3AAWG Recommends TLS

SSL or Secure Sockets Layer is protocol designed to provide a secure way of transmitting information between computer systems. Originally created by Netscape and released publicly as SSLv2 in 1995 and updated to SSLv3 in 1996. TLS or Transport Layer Security was created in 1999 as a replacement for SSLv3. TLS and SSL are most […]


The anatomy of From:

Compared with some of the more complex pieces of the email protocol the From: header seems deceptively simple. But I’ve heard several people be confused about what it’s made up of over the past couple of months, so I thought I’d dig a bit deeper into how it’s defined and how it’s used in practice. […]


Horses, not zebras

I was first introduced to the maxim “When you hear hoofbeats, think horses not zebras” when I worked in my first molecular biology lab 20-some-odd years ago. I’m no longer a gene jockey, but I still find myself applying this to troubleshooting delivery problems for clients. It’s not that I think all delivery problems are caused […]

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Ad-hoc analysis

I often pull emails into a database to analyze them, but sometimes I want something simpler. Emails are typically stored in one of two ways: mbox format, where an entire mailbox is stored in a single file, and maildir format, where a mailbox is a directory with one file in it for each email. My […]

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Weird mail problems today? Clear your DNS cache!

A number of sources are reporting this morning that there was a problem with some domains in the .com zone yesterday. These problems caused the DNS records of these domains to become corrupted. The records are now fixed. Some of the domains, however, had long TTLs. If a recursive resolver pulled the corrupted records, it […]


Post-mortem on the Spamhaus DOS

There’s been a ton of press over the last week on the denial of service attack on Spamhaus. A lot of it has been overly excited and exaggerated, probably in an effort to generate clicks and ad revenue at the relevant websites. But we’re starting to see the security and network experts talk about the […]

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More on the attack against Spamhaus and how you can help

While much of the attack against Spamhaus has been mitigated and their services and websites are currently up, the attack is still ongoing.  This is the biggest denial of service attack in history, with as much as 300 gigabits per second hitting Spamhaus servers and their upstream links. This traffic is so massive, that it’s […]

  • Lost in the mists of time

    Over on the Farsight Security blog Joe St. Sauver talks about some of the early days of online abuse, on usenet. Laura and I were on the periphery of early usenet abuse, mostly as users, but Usenet (and IRC) around then were the places we both started with email abuse.No Comments

  • Ongoing Yahoo delays

    I've been hearing from folks over the last few days that they're seeing an uptick in deferrals from Yahoo! The deferrals are not uniform. ESPs report they're seeing some, but not all, customers affected. Other ESPs aren't seeing any changes. It's not just you. But it would be very worthwhile to dig into engagement and other stats. It's possible this is a new normal at Yahoo! and they're tightening filters to catch mail that doesn't fit their standards but was previously difficult to filter.No Comments

  • AOL starts using Sender Score Certification

    Good news for Sender Score Certified IPs. Return Path recently announced that AOL has joined the list of ISPs offering preferential treatment to certified IPs.  1 Comment