Gmail filtering in a nutshell

Gmail’s approach to filtering; as described by one of the old timers. This person was dealing with network abuse back when I was still slinging DNA around as my job and just reading headers as a hobby.

Gmail uses a 10+ year old neural network that analyzes thousands of factors, related to email, IP, and web, integrated with all Google products, and with 99.9%+ accuracy for identifying certain types of messages, combined with an email-specific domain-based reputation system that combines IP reputation, content, read rates, reputation of other senders with similar content.

This excerpt was shared with a bunch of delivery experts and every one of them agreed. The Gmail filters are incredibly complex and they measure thousands of different things about email. Yes, sometimes you can remove a link or a URL and get mail to the inbox for a while. That doesn’t mean the block was against the URL, simply that changing the URL changed the score enough for the mail to go to the inbox.
This is part of what makes Gmail delivery issues so difficult to troubleshoot. There isn’t one thing, it’s all the things that contribute to where an email ends up. We, as senders and deliverability experts, don’t have access to the Gmail data. The poster goes on to say:

Trying to fix this using only inaccurate proxy data where there is no mediation pathway in a matter of weeks is complex.  We consume data from a multitude of sources, compile and analyze the data, determine which of the hundreds of factors we can influence should be adjusted, come up with the easiest plan to address the most influential factors, and explain that to the customer using the clearest language possible to individuals who are not educated on the definition of a complaint.

We do our best, with limited data and try and tell you how to fix things.
One of the biggest challenges with Gmail delivery is I am convinced they look at your profile of recipients. They can map someone who is collecting addresses through third parties, or buying lists based on the specific Gmail accounts targeted by a mailing. Gmail has publicly stated and has on their website that they don’t think co-reg or purchased lists are opt-in. They have the technology and ability to track that. I think it’s one reason senders trying to use email for acquisition have such a challenge getting into the inbox and Gmail. I think it’s a feature, not a bug for them.
 

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Thoughts on Gmail filtering

Gmail has some extremely complex filters. They’re machine learning based and measure hundreds of things about incoming mail. The filters are continually adjusting to changes and updating how they treat specific mail.
One consequence of continually adjusting machine learning filters is that filtering is not static. What passes to the inbox now, may not pass in a couple hours.
One of the other challenges with Gmail filters is that they look at all the mail mentioning a particular domain and so affiliate mail and 3rd party mail can affect delivery of corporate mail.
The good news is that continually adjusting filters adapt to positive changes as well as negative ones. In fact, I recently made a segmentation suggestion to a client and they saw a significant increase in inbox delivery at Gmail the next day.
Gmail can be a challenge for delivery, but send mail users want and mail does go to the inbox.

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July 2015: The Month in Email

Once again, we reviewed some of the ways brands are trying (or might try) to improve engagement with customers. LinkedIn, who frequently top lists of unwanted-but-legitimate email, announced that they’ll be sending less mail. Josh wrote about giving subscribers options for both the type and frequency of messages, and about setting expectations for new subscribers. In each case, it’s about respecting that customers really want to engage with brands in the email channel, but don’t want the permission they’ve granted to be abused. I also wrote a brief post following up on our June discussion on purchased lists, and as you’d predict, I continue to discourage companies from mailing to these recipients.

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IP reputation and email delivery

IP reputation is a measure of how much wanted mail a particular IP address sends.  This wanted mail is measured as a portion of the total email sent from that IP. Initially IP reputation was really the be all and end all of reputation, there was no real good way to authenticate a domain or a from address. Many ISPs built complex IP reputation models to evaluate mail based on the IP that sent the mail.
These IP reputation models were the best we had, but there were a lot of ways for spammers to game the system. Some spammers would create lots of accounts at ISPs and use them to open and interact with mail. Other spammers would trickle their mail out over hundreds or thousands of IPs in the hopes of diluting the badness enough to get to the inbox. Through it all they kept trying to get mail out through reputable ESPs, either by posing as legitimate customers or compromising servers.
These things worked for a while, but the ISPs started looking harder at the recipient pool in order to figure out if the interactions were real or not. They started looking at the total amount of identical mail coming from multiple IP addresses. The ISPs couldn’t rely on IP reputation so they started to dig down and get into content based filtering.
As the ISPs got better at identifying content and filtering on factors other than source IP, the importance of the IP address on inbox delivery changed. No longer was it good enough to have a high reputation IP sending mail.
These days your IP reputation dictates how fast you can send mail to a particular ISP. But a high reputation IP isn’t sufficient to get all the mail in the inbox. It’s really content that drives the inbox / bulk folder decisions these days.
 
Generally IPs that the ISP has not seen email traffic from before start out with a slight negative reputation. This is because most new IPs are actually infected machines. The negative reputation translates to rate limiting. The rate limiting minimizes people getting spam while the ISP works out if this is a real sender or a spammer.
Some ISPs put mail in the inbox and bulk foldering during the whitelisting process. In this case what they’re doing is seeing if your recipients care enough about your mail to look for it in the bulk folder. If they do, and they mark the mail as “not spam” then this feeds back to the sender reputation and the IP reputation.
If you’re seeing a lot of bulk foldering of mail, it’s unlikely there’s anything IP reputation based to do. Instead of worrying about IP reputation, focus instead on the content of the mail and see what you may need to do to improve the reputation of the domains and URLs (or landing pages) in the emails.

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