User Inbox Preferences - Gmail and Microsoft Deliverabilty Tips

Each mail receiver/spam filter has its own set of algorithms for receiving mail, so it can be a tricky to pinpoint the reason why a message was not received in the inbox (or other mailing classification folders). Gmail and Outlook/Office 365 tend to look at user-specific preferences when filtering mail (they look to see if the user typically opens the mail, moves it to a  folder, flags as spam, replies to the sender, etc). Completing sender authentication and maintaining a good sender reputation provides a good foundation for getting mail delivered to the inbox, but some mail filters go beyond those mechanisms and include user engagement.

Some examples of well-known inbox categories are the Promotions tab used in Gmail and the Clutter folder used in Outlook. Remember, these are not considered junk folders, but more like special inbox classification folders.

Unfortunately, there is very little a sender can do to guarantee placement to the inbox or "primary" folder, but below are some resources that can help you define how these particular user-defined preferences work.


Most filters tend to look at several different things

  • The sender ("from" address/IP address - good or bad reputation).
  • If sender authentication is in place (SPF/DKIM/DMARC).
  • If you're a bulk sender.
  • If the user has engaged in a two-way conversation.
  • The user's open rate.
  • If the user moves the message to the filtered folder or inbox.
  • The user classifies the message as a safe sender.


There are two key things a sender can do to encourage users to route mail to the Primary tab:

  • Separate different types of content with a unique "from" address, domain, and/or IP address. This gives users more options when classifying different types of mail (this could mean the difference between all of your mailings going to the Promotions tab versus some of your mailings going to the Promotions tab).
  • Encourage users to classify your mail as Not Spam, "star" them, or move them to a folder.  The mailings are more likely to end up in their inbox or Primary tab.

To learn more about Gmail bulk sender best practices, click here.

Outlook/Office 365

For Outlook and Office 365, Clutter and Junk mail are filtered prior to reaching the inbox. When receiving a message that meets the criteria for junk, Outlook/Office 365 places the mailing in the Junk folder. If not, it passes through any custom rules in place so that it can be classified in the corresponding folder. Next, Clutter analyzes the message based on the user's interaction history. Note that users have the ability to turn off clutter or to adjust its settings to prevent messages to be classified as such.

To learn more about how Clutter classifies mailings, click here.

Sender Advice

Below are a few things that senders can do to help with inbox delivery:

  • Complete sender authentication (SPF and DKIM).
  • Keep your messages consistent with your "from" address.
  • Send to opted-in and engaged subscribers only.
  • Encourage subscribers to interact with your messages.
  • Ask subscribers to add your email address to their safe senders list to ensure delivery.