Filtering secret sauce

It seems one of the most asked questions I hear from people is about filters and what the secret sauce is.

Cloudmark’s processes which determine which IPs get a poor or suspect reputation in our CSI products, take into account many different factors, including both spam trap hits and volume of trusted end user complaints (hitting the “This is spam” button), reputation of the reverse DNS of the IP, reputation of the IP block that the IP is part of, and traffic volumes over time which help measure likely use of the IP in a snowshoe attack.
ISPs primarily want their email infrastructure to stay available and performing well, and for email recipients to receive the email that they want to receive. But if as a sender or marketer your email is going to spamtraps or people are hitting the “This is spam” button, then it’s not going to people who want it. Email blacklists and Cloudmark’s Sender Intelligence

Cloudmark is saying all the things deliverability experts tell senders. Maybe hearing it direct from the source will make the message stick better.

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The take home message? Pay attention to what is being sent and who it is being sent to. This is nothing new, but many marketers seem to forget it in the effort to get into their customers’ inboxes.

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Engagement, it's not what you might think

Most delivery experts will tell you that ISPs measure recipient engagement as a part of their delivery. That’s absolutely true, but I think there’s a language difference that makes it hard for senders to understand what we mean by engagement.
ISPs, and other filtering companies, profile their user base. They know, for instance, who logs in and checks mail every day. They know who checks mail every 20 seconds. They know who gets a lot of spam. They know who hasn’t logged in for months. They know who accurately marks mail as spam and who is sloppy with the this-is-spam button. They know if certain recipients get the same mail, it’s likely to be spam.
Engagement at the ISPs is more about the recipient engaging with their email address and the mail in their mailbox then it is about the recipient engaging with specific emails.
 

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SMTP Level Rejections

While discussing a draft of a Deliverability BCP document the issue came up of what rejections at different phases of the email delivery transaction can mean. That’s quite a big subject, but here’s a quick cheat sheet.
At initial connection
Dropped or failed connection:

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