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When it comes to why campaigns get marked as spam, most ISPs are regarded as “black boxes”. But recently, Gmail’s Anti-Spam Team bucked that trend, by demystifying much of what they’re doing behind the scenes. I’ve summarized the key points from our discussion to help emailers improve their chances at inbox placement, as well as get the inside story on how spam filtering works.

Keeping in mind that ISPs very rarely discuss how they operate, it was an honor to be invited to talk with Sri Somanchi on Gmail’s Anti-Spam Team, on behalf of the ESPC, a group comprised of many of the most popular email service providers. While Sri was understandably mum on many of the technical aspects of Gmail’s operations, he did have some great advice on how to keep our campaigns out of the Spam folder. To start things off, we asked:

Why do emails get sent to the Spam folder?

So, you’ve just sent an email campaign and are about to kick back with your favorite beverage, when you receive a message from a subscriber… Letting you know that your campaign has gone into Gmail’s ‘Spam’ folder. Regardless of whether you have 5 or 5,000 subscribers using this webmail client, such an event can be a perplexing experience.

On Gmail’s end, Sri revealed that there are literally hundreds of signals to decide whether an email should go to the Inbox or the Spam folder. The importance of any given signal is dynamic and determined on complex algorithms, in essence it means that one factor or another isn’t likely to bin an entire campaign and there is no point in obsessing over any one element. “Think of how you can make the user love your mails rather than how to land in the Inbox” was Sri’s basic advice on the subject. Essentially stating if the user likes your mail the spam filter should not stop it from getting to the Inbox.

The takeaway here is that we shouldn’t simply lay the blame on say, a couple of lines of copy when campaigns go south and instead, take a more holistic view towards improving our email programmes. It is therefore better to focus on why a user might have marked an email as spam and NOT why the spam filter did not put you in the Inbox.

Helpfully, Sri highlighted two things in particular which can make or break your campaign sends.

What can I do to improve inbox placement?

Not wanting to leave anyone hanging, we discussed the most important things that senders should focus on to stay out of Spam. Sri revealed that Gmail takes email engagement very seriously. Whilst Sri would not go into details behind how Gmail classifies a message it is evident he and the Gmail Anti-Spam team want to see evidence that your recipients love or at the very least, want your messages, for them to reach the inbox.

As marketers, we look at metrics such as opens, reopens, replies, forwards and other positive interactions. These interactions generally give an indication the recipient is happy with the content and this in turn reduces the probability of your message being marked as spam. Sri did say if users do not mark something as spam, there is little reason for filters to flag future emails. Also, ensuring that the engagement levels are high, will lead to users moving mails accidentally misclassified by Gmail back to Inbox, which will help their systems to learn and correct themselves.

The implication for senders like ourselves is that we have to focus on designing campaigns that recipients love and engage with, ensure you make it as easy as possible for your recipients to do so – one thing that you could do is to feature strong call-to-actions, or ask subscribers to reply directly if they’d like to get in touch with you.

The second piece of advice was quite unique – that was whilst a frequent sending pattern might be tolerated initially, eventually recipients will tire of the frequency.

Based on Sri’s experience we learned sending frequency at times is the biggest reason for users being turned off by your email program. If you do not adopt engagement based sending , a frequent sending pattern might be tolerated initially, but eventually recipients will tire of the frequency and start marking your mail as spam.

Engagement and frequency aside, setting up email authentication was also noted as being important for email marketers. If you use a custom domain, managing your own authentication by adding DKIM records to your DNS is essential (we authenticate emails sent from your account by default). A willingness to work with email service providers to resolve any deliverability issues was also highlighted, whether these are reported internally, or via third-parties such as Gmail’s Feedback Loop. All these factors go to show that while content is commonly looked at as the trigger for spam complaints, it’s one of many things that may factor in some, perhaps even small way, in the determination as to whether your campaigns should get placed in the inbox.

A huge thanks to Sri and Gmail’s Anti-Spam Team for being so open about Gmail’s approach to combating spam and abuse, as well as how legitimate senders can stay in the clear. For more on how junk mail filtering works and what you can do to improve your campaigns, take a look at our Guide to Landing in the Inbox. We’re also happy to answer any questions you may have, too.

  • Zulh

    A very detail & comprehensive explaination about this new Gmail feature. It seems like Google is taking serious approach to ensure their users feel happy using Gmail services and we (marketers) should accept it.

  • Kent McGovern

    I see you highlighted DKIM and SenderID for authentication, Microsoft themselves don’t look at SenderID anymore, did you mean SPF?

  • Andrew Bonar

    Thanks Kent!
    I had meant only DKIM (albeit SPF is still very useful and SenderID redundant), unfortunately the complete title from an old blog post was included.

  • Tim Kastner

    I’m glad to see Gmail going on record indicating the importance of engagement. I speak with so many marketers who think engagement is a myth and it’s strictly about reputation.

  • Andrew Bonar

    Agreed Tim, its great as a deliverability person to be able to say with absolute certainty that engagement matters. It is something we have all known from experience, but this is ‘from the horses mouth’ so to speak and leaves no doubt in the mind…

    As long as you have a permission based list: your reputation will be defined by lack of complaints and engagement. A good reputation will ensure high inbox placement.

  • Bluegill 4 me

    Since about the time Gmail started the Promotions tab, its antispam efficacy has suffered. At least once a day, I get a spam of the same general type. A typical example of a subject is, “Worried?Losing-Your-hair? -$250Gift-Certificate.”

    I report these as spam as soon as they show up, to no avail. If any of your antispam people want to talk to me about those or even use my mailbox for beta antispam rules, I’m in. I worked for years in antispam (both as a postmaster at an ISP, and later, at an antispam vendor; I still work there but am on the web security team now) so I know this can be fixed and hope it will be. Gmail’s efficacy used to be flawless, at least for me.

  • Sai Krishna M

    I thought its hard to understand gmail’s algorithm on sending mails into spam folder, but I got a idea about it after reading your informative article, thanks for your research.

  • cblemuel

    Correct me if I’m wrong. Do you think these will help?

    Running a promotion/contest/survey – and have them reply directly to email sent

    :: We’ll need subscribers interact to our email by have them reply directly to our emails.

    1. in gmail they are looking for patterns of interactions (noted on #1). When a subscriber reply to our emails the To: recipient will be directly added to “Most Contacted” and “Other contacts” group. This means a subscriber sending information to gmail on “Engagement Metrics – replies”. And most likely will help us getting through inbox.

    2. Let say the subscriber hit “Report Spam” before and we send an email that needs his/her reply, when they reply -a notification bar will display telling subscriber why it drop to spam and possibility then they would click the “Not spam” button – that is if they want to get the our replies or future messages to their inbox.

    Hitting “Not Spam” button means sending signal to Gmail that the user love emails and want messages from the “sender” to drop to inbox folder.

    What to do next?

    – Run a promotion/contest/survey that need their reply in exchange of gift cards, discount or any other forms of rewards.
    – or any other means just to have them reply

    Important Notes:

    – The from address should be monitored (during promotion/contest) – all replies should be recorded.

    – The From and Reply-to should be the same

  • Andrew Bonar


    Whilst Gmail did not speak directly to tactics, and I did press them on this.. Those all seem like very solid ideas.

    One thing Sri did talk off was “Hitting “Not Spam” button means sending signal to Gmail that the user love emails and want messages from the “sender” to drop to inbox folder.”

    I haven’t got the recording to hand, but something along the lines of ‘reporting not-spam’, sends a signal in orders of many magnitude of ‘reporting spam’ – I am sure they have many ways to ensure that is not gamed however.

  • Dan

    Great insight!

  • Ben

    Nice1 Andrew
    Catch up for a beer soon eh

  • John

    Good stuff. Thanks to you & the CM team for helping us to improve inbox placement.

  • Andrew Bonar

    Thanks for all the kind comments, always happy to try and help.

  • Andrew Bonar

    @Ben – soon I hope!

  • Ewout Winkelman

    Interesting read, thanks!

    Good to hear Google takes this approach, since it’s all about keeping the end-users happy. If they’re happy, we’ll be happy also.

  • Derek Stevenson

    Has anyone noticed how spam is getting through gmail’s spam filter with words being strung together like:

    GetYour2014creditReport-and scoreInstantly




    Alert_Your 2 0 1 4 creditScoreMay have beenUpdated


    These styles of messages started hitting all of my gmail accounts recently. Even gmail accounts I use specifically for google analytics as they have limits on the amount of accounts you can have. I have never given out these email addresses too anyone. This has been going on for roughly around 2 months now and I always mark them as spam but they still hit the inbox.

This blog provides general information and discussion about email marketing and related subjects. The content provided in this blog ("Content”), should not be construed as and is not intended to constitute financial, legal or tax advice. You should seek the advice of professionals prior to acting upon any information contained in the Content. All Content is provided strictly “as is” and we make no warranty or representation of any kind regarding the Content.
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