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The importance of data hygiene

Over the weekend, one of the major ISPs purged a lot of abandoned accounts from their system. This has resulted in a massive increase in 550 user unknown bounces at that ISP. This ISP is one of those that uses bounces to feed into their reputation system and the purge may cause otherwise good senders to be blocked temporarily.
Talking to clients and other industry folks, it looks like the addresses that have newly bounced off had zero activity for at least 6 months. Nothing. Nada. No clicks. No opens. No interaction.
This is why data hygiene is so critical. Just because the emails are being accepted at the ISP, and even showing inbox placement at the mailbox monitoring companies does not mean that there is actually someone reading your email. Failure to look at overall data means that when an ISP bulk deletes abandoned accounts then bounces will increase. While I don’t expect this to have any real, long term effect on sender reputation I do expect that some senders with a lot of cruft on their list will see some short term delivery problems.
Companies that run re-engagement campaigns saw a whole lot less bouncing and even less blocking as a result of the purge. They were removing addresses that were non-responsive all along and thus didn’t have major deadwood on their list.
Ongoing data hygiene shows you what your list really is, not your list plus abandoned accounts. The addresses that the ISP purged? They were not valuable anyway. No one was reading that mail for at least 6 months.
If you did see a spike in bounces this weekend at a major ISP, you should really look at engagement. If some percentage of recipients at one ISP are actually non-existent, then it’s likely that about that same number are non-existent at other major ISPs as well. What are you going to do to identify and remove those dead addresses from your lists?

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Why do ISPs do that?

One of the most common things I hear is “but why does the ISP do it that way?” The generic answer for that question is: because it works for them and meets their needs. Anyone designing a mail system has to implement some sort of spam filtering and will have to accept the potential for lost mail. Even the those recipients who runs no software filtering may lose mail. Their spamfilter is the delete key and sometimes they’ll delete a real mail.
Every mailserver admin, whether managing a MTA for a corporation, an ISP or themselves inevitably looks at the question of false positives and false negatives. Some are more sensitive to false negatives and would rather block real mail than have to wade through a mailbox full of spam. Others are more sensitive to false positives and would rather deal with unfiltered spam than risk losing mail.
At the ISPs, many of these decisions aren’t made by one person, but the decisions are driven by the business philosophy, requirements and technology. The different consumer ISPs have different philosophies and these show in their spamfiltering.
Gmail, for instance, has a lot of faith in their ability to sort, classify and rank text. This is, after all, what Google does. Therefore, they accept most of the email delivered to Gmail users and then sort after the fact. This fits their technology, their available resources and their business philosophy. They leave as much filtering at the enduser level as they can.
Yahoo, on the other hand, chooses to filter mail at the MTA. While their spamfoldering algorithms are good, they don’t want to waste CPU and filtering effort on mail that they think may be spam. So, they choose to block heavily at the edge, going so far as to rate limit senders that they don’t know about the mail. Endusers are protected from malicious mail and senders have the ability to retry mail until it is accepted.
The same types of entries could be written about Hotmail or AOL. They could even be written about the various spam filter vendors and blocklists. Every company has their own way of doing things and their way reflects their underlying business philosophy.

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Gmail and the PBL

Yesterday I wrote about the underlying philosophy of spam filtering and how different places have different philosophies that drive their filtering decisions. That post was actually triggered by a blog post I read where the author was asking why Gmail was using the PBL but instead of rejecting mail from PBL listed hosts they instead accepted and bulkfoldered the mail.
The blog post ends with a question:

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