Inbox Investigation: Inside Gmail’s Customized Inbox

HIPB2B delivered approximately 48 million emails last year. We’re always trying to understand what happens when our emails hit the inboxes of our customer’s target audiences.

What works? What makes it to the inbox? Where else could the email get sent? How can we make sure our emails hit the inbox? Those are the questions our running series, “Inbox Investigation” will answer in the coming weeks. We’ll hit on all the most popular inboxes, unboxing how and where email is delivered.

First, we tackled Outlook. That brings us to our second email client. Today, we dig into Gmail.

Gmail is supposedly the result of Google’s former, current, or past “20 percent policy.” That was this mythical idea that one day a week, Google employees could work on a side project they thought would benefit the company. It’s the second most popular of email services and has a user base of over 1 billion people.

It was launched in 2004, and the developers keep tweaking the web app over time.

Gmail is well-known for its anti-spam filters, which have only gotten better as both Google’s algorithms and technology has advanced.

As many as 27% of all emails are opened in Gmail, according to Litmus’ running email client monitor. That might be because between the web app and the mobile app, you can open just about any email address through Gmail.

They estimate that 890 million emails were sent in December 2018. That means that 240,300,000 emails were sent to Gmail inboxes in that month.

There are two markers for users to customize their inbox experience and teach Gmail what they want to see more of.



Some messages are automatically marked Important by Gmail. This is mostly based on past user actions.

If users open and reply to emails from a sender, they will show up in their inbox as Important (yellow colored arrow) and will be delivered to their Primary inbox. Something marked Important will be colored yellow, as you can see in the header. You can click this to remove the yellow filling.

But wait, there’s one more aspect to this. Do you notice the example has >> inside the arrow? Well, there are a few options for this.


Ignoring the coloring, do you see how each of these important markers have either two symbols, one symbol, or nothing?

What does that mean? Let’s break that down too:



These are message only sent to you

 These are messages sent to your email address (not a mailing list)

These are messages sent to you as part of a mailing list.


As an email marketer, your emails will likely show up blank. You can and should encourage your recipients to click the arrow to mark it as Important if they want to see your content in their inbox.



This is just a user action. Users can choose to “star” certain emails. From what I read, it seems like you could customize the coloring of the stars at one point.

That doesn’t seem to be an option now.


Action Items

Now hover your mouse over a message in your inbox. To the right side, there are a handful of icons here that users can use to act on the email they’ve just received.

Let’s quickly investigate those too, since they are another way your subscribers can interact with your message in Gmail.


Archive – This moves a message from a user’s inbox to the “All Mail” tab located when they open the “More” section. Emails that are archived are not easy to find. This is a user action only.


Trash – This obviously moves this email from the inbox to Trash.


Mark as Read – Another obvious one. It is good to note that this action will likely trigger any tracking pixels that measure opens. Users do not need to open a message to Mark as Read.


Snooze – This one is very interesting. It allows users to see an email and snooze it for later. The user can pick when they see the email again.

Beyond all these markers and actions, you can take there are also a plethora of options for how users view their inbox. That made this inbox investigation challenging, but interesting.

From what I could gather there are two different sets of options for users to customize.


Gmail Inbox Types

To access this setting, users must look towards the “Inbox” icon in the top right corner. If you hover your mouse over it, a small white arrow appears, as pictured above.

From there, you’ll see a variety of inbox types.



This is the view that users start with. Google puts the following message for this one.

The Default view seems to order first by priority, which I assume comes from the machine learning engine that helps filter Gmail inboxes. Then it also has some data-based filtering, ensuring that you see the most recent emails in your inbox.

This also is the option that creates the tabs you’ll read about in the next section.


Important first

This one is obvious. The Important view groups all the messages that either the user or Google algorithm has decided is important. That means yellow arrows will dominate a user’s Inbox if they choose to view it that way.

The rest of the messages appear below ones marked Important.


Unread first

Any unread messages that aren’t spam will appear in the inbox on top, with all read messages below them.


Starred First

This view is also very easy to understand, any emails that users star will be given top priority in the inbox.


Priority Inbox

In this inbox, you see all Important and unread emails in your inbox first.

Inbox Tab Options

Users will only see this in the “Default View” mentioned above. They will have to change the view to eliminate these tabs, so most users will see them.

Users are given three tabs by default. They are Primary, Social, and Promotions. Users can also go into their settings and click Update and Forums.



These are emails that Gmail chooses based on past interactions and sender type. You’ll see a lot of emails that are to you personally, on lists from people you know personally, and emails from mailing lists that you often open.



These are emails from social networks. It nicely tucks away user’s social stuff so it’s not cluttering up their Primary inbox.



This is likely where your marketing emails end up, which also means that this is often one of the more crowded tabs. There are numbers next to these tabs to show how many emails have arrived.



Here users will find updates from credit card companies, job hunting sites, their bank, and more.

This of this as the place where practical emails are sent by organizations to users.



This category covers any non-social media related conversations you’ve had on forums. I also have some mailing list items on mine from smaller organizations.


Notification settings are entirely up to the user. There are three options that the user can choose for their notifications on Gmail’s web app.

Not that no desktop notifications are enabled by default. The users choose whether or not to see these on their computers.

Even if notifications are on, users won’t see them for anything besides the Primary tab (or just the regular inbox if they’re using another inbox view).

There’s another option to see only notifications that are Important.


Gmail is notorious for its aggressive, intelligent spam filters. Many people chose to sign up for it back during its initial creation in 2004 for the spam filters.

Gmail has a highly aggressive spam filter. It will start to push emails from brands you don’t interact with into the spam box. It also learns from the interactions of other users and a brand. If a lot of people aren’t engaging with your content or someone marks you as spam, those interactions might start sending your brand to the spam box for everyone.

In essence, on the desktop, most users will only look at what’s marked Important and what falls in their Primary inbox. So how do you get your content into those places?

What does this mean for marketers?



I said it before, and I’ll say it again. You need to ask your subscribers to interact with your emails to ensure they’re not sent to one of Gmail’s alternate boxes to be buried.

Tell them to look for you in their Promotions tab once they sign up for your mailing list. Then ask them to mark your email as Important or to move it to their Primary inbox.


Write Snappy Subject Lines

Emails that users interact with are in. By in, I mean in the inbox.

Make sure that your subject lines stand out from all the other ones sitting in Promotions tabs. Cram them filled with emotionally-loaded language and promised value.


Pick Perfect Send Times

This was a tip I also gave in the last inbox investigation post. Figure out when users most open their emails.

Send emails to them during that time, or on off times when you know that other companies in Promotions will not be sending. It helps your marketing messages get seen.



Now, you understand how many different places and ways your emails can land in a Gmail inbox. What can you learn from this?

Gmail is already using features like smart compose in their inbox and reminders to follow up on emails it deems important. How do you think these features will change how your marketing messages are received?

Let us know what you think.



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