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Category: Technical

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. […]

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If you have servers using SSL, read this

I was going to post about SSL certification and setup today, but the security world got ahead of me. Recent versions of openssl – the library used by most applications to implement SSL – released over the past couple of years have a critical bug in them. This bug lets any attacker read any information […]

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More denial of service attacks

There are quite a lot of NTP-amplified denial of service attacks going around at the moment targeting tech and ecommerce companies, including some in the email space. What does NTP-amplifed mean? NTP is “Network Time Protocol” – it allows computers to set their clocks based on an accurate source, and keep them accurate. It’s very […]

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Open relays

Spamhaus wrote about the return of open relays yesterday. What they’re seeing today matches what I see: there is fairly consistent abuse of open relays to send spam. As spam problems go it’s not as serious as compromised machines or abuse-tolerant ESPs / ISPs/ freemail providers – either in terms of volume or user inbox […]

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Compromising a Mail Client

Your entire work life is in your work mail client. All the people you communicate with – co-workers, friends, family, vendors, customers, colleagues. Every email you send. Every email you receive. Any files you attach or receive. If someone can compromise your mail client, they can see all that. They can save copies of all […]

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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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SPF Fail: too many DNS lookups

I’ve had a couple folks come to me recently for help troubleshooting SPF failures. The error messages said the SPF record was invalid, but by all checks it was valid. Eventually, we tracked the issue down to how many include files were in the SPF record. The SPF specification specifically limits the number of lookups […]

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New top level domains

ICANN have signed agreements for four new top level domains, all internationalized domains from the 2o12 applications for new TLDs. They are شبكة (“network” or maybe “web” in arabic), 游戏 (“game” in chinese), онлайн and сайт (“online” and “website” in russian). It’ll take a while for the registries to ramp up their infrastructure, but you might start seeing […]

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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 […]

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What is a dot-zero listing?

Some email blacklists focus solely on allowing their users to block mail from problematic sources. Others aim to reduce the amount of bad mail sent and prefer senders clean up their practices, rather than just blocking them wholesale. The Spamhaus SBL is one of the second type, using listings both to block mail permanently from […]

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  • AOL problems

    Lots of people are reporting ongoing (RTR:GE) messages from AOL today.  This indicates the AOL mail servers are having problems and can't accept mail. This has nothing to do with spam, filtering or malicious email. This is simply their servers aren't functioning as well as they should be and so AOL can't accept all the mail thrown at them. These types of blocks resolve themselves. No Comments


  • Fixing discussion lists to work with new Yahoo policy

    Al has some really good advice on how to fix discussion lists to work with the new Yahoo policy. One thing I would add is the suggestion to actually check dmarc records before assuming policy. This will not only mean you're not having to rewrite things that don't need to be rewritten, but it will also mean you won't be caught flat footed if (when?) other free mail providers start publishing p=reject.No Comments


  • Sendgrid's open letter to Gmail

    Paul Kincaid-Smith wrote an open letter to Gmail about their experiences with the Gmail FBL and how the data from Gmail helped Sendgrid find problem customers. I know a lot of folks are frustrated with Gmail not returning more than statistics, but there is a place for this type of feedback within a comprehensive compliance desk.No Comments


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