Read Time: 14 min

Delivering Ep. 15: How Gmail Detects Spam and Some Industry News

In this episode of Delivering, host Jason Rodriguez digs into how Gmail classifies messages as spam before looking at a potentially disruptive new email service and the state of email surveys in 2020.

Episode Transcript

Welcome to Delivering, a podcast about email design, strategy, copywriting, development, and the email marketing industry. I’m your host, Jason Rodriguez. Delivering is brought to you by Litmus—the only platform trusted by professionals to help you send email with confidence, every time. Over 600,000 marketing professionals use Litmus’ tools to build, test, and analyze better email campaigns faster.

Head over to to start your free 7-day trial of Litmus, and start sending better emails today.

Be sure to subscribe to Delivering on iTunes or Spotify to listen to future episodes and join the conversation on Twitter using the hashtag #DeliveringPodcast.

The other week, someone on Twitter—sorry, I don’t remember who—linked out to an article from Google that shed some light on how Gmail detects and categorizes spam. In fact, the title of the article is Prevent mail to Gmail users from being blocked or sent to spam. Catchy, right?

The article used to be called the Bulk Sender Guidelines and lives under a help section on sending bulk email. As most email marketers think of what they do as “marketing” and not “bulk sending”, it’s no surprise that I was unfamiliar with this article or its previous incarnation. I’d wager that most email marketers are unaware of it. Which is a shame, since it’s an interesting read.

With that in mind, I thought it’d be a good idea to go through the article in order to gain some insight into how Gmail classifies messages as spam. Sound good? Cool, let’s go.

The first thing email folks should note is that Gmail makes it very clear up front that, even if you follow all of the recommendations in the guide, there’s no guarantee that your messages will be delivered to a subscriber’s inbox. It’s also interesting that Gmail distinguishes between different levels of action it will take towards suspect messages.

It’s not just marking a message as spam. Although Google may do that, in which case the message will go into a subscriber’s spam folder, Gmail may throttle the delivery of messages over time or outright block your message from being delivered. That probably sounds scary for most subscribers, which is even more reason to follow Gmail’s guidelines.

OK, getting down to what the guidelines actually are…

Broadly speaking, Google has three categories that contribute to spam classification: Sending guidelines—which are kind of like deliverability best practices—engagement, and message formatting. Fortunately, there aren’t too many surprises in any of those categories.

When it comes to sending messages, what have been traditionally recognized as best practices still apply.

Marketers should send all messages from the same IP address for their company and your server should use authentication like SPF records, DKIM signing, and DMARC records to help ensure deliverability. All of these are usually handled by or with the help of your email service provider, so check with them if you do find yourself running into issues and you think it’s related to authentication.

One recommendation that Google makes which I found interesting is the use of the “from” field in the headers of an email. Senders can specify which email address is doing the sending. While a lot of companies send from something like “”—which is bad for a number of reasons—Google recommends matching the from address to the content and purpose of your email campaign.

For example, if you’re sending a purchase receipt email, you could use If you’re sending promotional emails, like a lot of us do, then would be best. Or, if there’s an account-related notification, is recommended.

I personally don’t see many companies actually doing that. At Litmus, we use different subdomains for different types of messages (and ESPs), but typically use the same name of “Hello” before that at symbol. Most stuff I see in my inbox follows that same convention. We haven’t seen any deliverability or spam hits from Google for going against that recommendation, so I’m curious how much it figures into their algorithm. Would setting up these different addresses improve deliverability to Gmail? Or help with proper classification within Gmail’s different tabs?

Google’s engagement recommendations are almost entirely organized around making it easy for people to unsubscribe from emails. Here, their advice is golden:

  1. Include a prominent link in the message that takes users to a page for unsubscribing.
  2. Let users review the individual mailing lists they’re subscribed to. Let them unsubscribe from lists individually, or all lists at once.
  3. Automatically unsubscribe users who have multiple bounced messages.
  4. Periodically send a confirmation message to users to make sure they still want to get your messages.

Email marketers should get out of the outdated and horrible practice of trying to hide unsubscribe links in emails. Stop making them small, confusing subscribers by making them look like surrounding text, or calling them something that they aren’t. Embrace unsubscribes as a natural part of maintaining a healthy email list.

I really like the second recommendation, too. Google is, in effect, recommending that senders maintain a preference center to give subscribers nuanced control over what they receive. This is an excellent idea and one we’ve been advocating for a long time. If you haven’t implemented a preference center for your subscribers, now’s the time to do it.

And, as made clear in recommendation number 4, re-permission campaigns are a great tool to maintain consent over a long term with subscribers and something that Gmail looks at when grading the reputation of senders.

It’s no surprise that Google recommends implementing one-click unsubscribe, too. As one of the original supporters of list-unsubscribe, Gmail would naturally love to see senders add the appropriate headers to email campaigns to make it easier for subscribers to opt-out of future campaigns. Since list-unsubscribe does involve updating your email headers, you may need to talk with your ESP about configuration if they aren’t already supporting it.

Beyond that, Gmail’s recommendations make sense and should be familiar to anyone paying attention to the email landscape for the last few years, especially post-GDPR. Don’t purchase email lists from anyone, don’t send emails to people that didn’t sign up, and don’t pre-check consent boxes on your forms. If you’re not following those guidelines already, please, please, please start now.

Finally, Google has some recommendations for the actual formatting of messages.

When it comes to development, email designers should be formatting proper HTML. The spec that Google links to uses the HTML5 doctype. While a lot of templates still use legacy doctypes, like the XHTML transitional one, you’re probably safe updating things for futureproofing. Unless, of course, you’re seeing rendering artifacts in older email clients with the HTML5 doctype.

Content-wise, there are three key recommendations. The first is that the subject line should be relevant to the content of the message and not misleading. This is clearly defined in the CAN-SPAM law in the US and should be standard practice at this point. Unfortunately, senders still write misleading subject lines or use tricks like the “reply” subject line. Can we all stop now that it’s 2020?

Next is that links within an email should be not only be visible and easy to understand, but that they should make it clear where a subscriber will be taken when the link is clicked. I love this, not only as an email user, but for the accessibility affordances it implies. To me, this means that designers should use visual indicators—beyond just color—to make links clear. Bolding and underlining links, or making main calls-to-action look like buttons, help everyone—especially those with different abilities—actually use an email. It also means that we should stop writing shitty copy for links like “click here” or “read more”. Describe what happens when you click on something or what a subscriber will actually be reading. Not only could it help with deliverability in Gmail, but it will almost certainly help with engagement and conversions, too.

Finally, one of the most important recommendations from Gmail is that you shouldn’t use HTML and CSS to hide content in an email, as that could result in an email being marked as spam.

This is potentially huge, as using CSS to hide content is very useful—especially for mobile emails (think hamburger menus or accordions) and in interactive email campaigns. Or think about preview text. We use CSS to hide preview text that we want pulled into the inbox view but not the message view itself.

Does this mean that Gmail will start marking completely valid, relevant, and useful messages as spam just because we use CSS to hide content in a thoughtful way? I’m not entirely sure. I think this is one of those recommendations that we’ll have to keep an eye on, as it’s not clear in this article what kinds of HTML and CSS techniques are OK and what kinds are deemed malicious by Google.

Overall, it’s an interesting article to pick through. There are a few links to supplementary resources, too, so take some time with it to see if you can get more out of your email campaigns for Gmail users.

In other industry news, software company Basecamp announced that it will be releasing a new email service called HEY sometime in April. They somehow secured the domain, which I’d love to know how much they paid for that one.

What’s interesting is that Basecamp is very outspoken when it comes to privacy and ethical software development, which is awesome. If you’ve read any of their books or followed along with the Signal v. Noise blog, which has been around forever, you’ll know where they’re coming from.

Basecamp co-founder, David Heinemeier Hansson or DHH, took to Twitter for the announcement. I think it’s worth quoting him in full:

The first brand-new product from us at Basecamp in many years is coming this April: An email service built for people who both love and hate email. We’ll fix the hate, and leave you with the love. Email is amazing, and it deserves our best.

Email is so damn good that we have to rescue it from the travesty that is its capture by the likes of Gmail, Outlook, and a handful of other big tech providers. They’ve successfully fooled everyone into thinking the highest ambitions in email is a new Gmail client. Ugh.

So with HEY, we’re going full stack and full integration. An email service that doesn’t require paying fealty to Google or Microsoft or anyone else. A new, fresh way to cut that big tech umbilical cord.

It’s unclear as to what all of that means, though. The landing page for HEY is simple and vague. In subsequent Tweets, though, DHH praises other email services like FastMail and ProtonMail—both of which are focused on security and privacy. DHH has also been very vocal about email marketers using tracking pixels to track subscriber behavior.

My guess is that HEY will be a stripped down, minimal email client that strips email tracking and uses its own algorithms to filter out marketing emails from personal communications. I’m curious to see if HEY will completely block marketing emails—which would be extreme but kind of inline with DHH and Basecamp’s philosophy—or if it’ll just silo them into separate folders like Gmail’s tabs.

One important clue is in a response from DHH to the question of whether or not HEY will support HTML and CSS or custom fonts. His reply?

As little as possible and absolutely not.

I think this is indicative of what to expect – something focused on the “love” in email and using it as a medium to build relationships. From my understanding, DHH and crew don’t think that marketing emails are about love, just selling, so they’ll do as little as possible to support email marketers in favor of making email more personal again.

The last few years have seen a massive uptick in personal newsletters, curated digests, and more thoughtful email publications from senders big and small, though. None of those fall into the bucket of traditional email marketing, so I’m wondering where that will fit in with HEY’s philosophy.

Again, details are scarce but my interest is piqued. You’d better believe that I sent a story about how email has changed my life in the hopes of getting early access.

Finally, I wanted to mention a survey going around that I encourage everyone to take. Litmus designer and all-around email geek Dylan Smith launched The 2020 Email Geeks Salary Survey, which you can take at Dylan, who helps run the Email Geeks Slack channel, is collecting anonymous salary info to help provide transparency in the industry.

The survey is quick to take and asks about your job and role, salary, bonuses and benefits, and then demographic information. It’s a great way to get a look at the makeup and pay disparities across the industry and could become good fuel for getting paid what you’re worth.

We all know that email marketing is routinely undervalued, despite the absurd ROI it provides. It’s interesting now to see just how undervalued. As of recording, there are over 400 responses with an average annual salary around $76,000 USD. While that may seem substantial, there are some pretty big salaries at the high end skewing that and it’s still under the $92,000 average salary that Glassdoor reports for software engineers. While email marketing encompasses a ton of different roles—some of which aren’t 1-to-1 comparisons of software engineering—email marketers are increasingly required to have in-depth technical and specialist knowledge that, many times, has a greater business impact than software engineering roles.

I’m looking forward to the full report from the Email Geeks community and a more open conversation about salaries, benefits, and value throughout the email industry.

That wraps it up for this week. Be sure to subscribe to Delivering on iTunes or Spotify to listen to future episodes and join the conversation on Twitter using the hashtag #DeliveringPodcast.

If you could give us a review, that’d be amazing, too.

And be sure to head over to to start your free 7-day trial of Litmus—the only platform trusted by professionals to help you send email with confidence, every time. Over 600,000 marketing professionals use Litmus’ tools to build, test, and analyze better email campaigns faster. Go to to start your free 7-day trial of Litmus, and start sending better emails today.

Jason Rodriguez

Jason Rodriguez

Jason Rodriguez was the Community & Product Evangelist at Litmus