How does email sorting decide which tab an email goes in?

Answer first

Email sorting decides which tab each wanted email goes in: the main inbox, promotions or updates. It is not deciding whether mail is junk; a spam filter does that. It looks at clues such as who sent it and what it says. Mail that mixes the clues can land in the wrong tab.

In one line: A program that puts each wanted email into a tab, such as the main inbox, promotions or updates.

Last reviewed: 25 October 2026 3 min read

What decision does it make?

Every wanted email gets exactly one tab. Unlike a spam filter, which asks yes or no, the sorter picks one answer from several. Tab names differ between email apps.

Decision	Possible answers
Which tab does this email go in?	Main inbox: mail from people you know. Promotions: ads and deals. Updates: receipts, bills and statements.

What does it look at?

Sender. Mail from a person you write to is different from mail sent by a shop or a club.
What it is about. Ads, deals and newsletters point to promotions; receipts, bills and statements point to updates.
Your moves. When you move an email to another tab, the sorter learns where mail like it should go.

How does it learn the rule?

Collect sorted examples. Start with many emails that already have the right tab as a label.
Find the clues. The program learns which senders and kinds of message show up most in each tab.
Sort new mail. Each new email goes to the tab whose clues it matches best.
Learn from moves. When people move an email to a different tab, that is a new example to learn from.

Where can it go wrong?

A person mentions a sale. "There is a sale at the bike shop, want to go?" can look like an ad.
A needed email gets buried. A receipt or a school notice in promotions is easy to miss.
The same word, a different meaning. A school bake sale is not a shop deal, but both say "sale".

Try it

Toy example: pick the rule that puts every ad in the Promotions tab and nothing else. Then test your rule on new emails.

Toy example: emails described in words, the clues each one has, and whether it really belongs in Promotions.

Item	Values	Right move or bin
Email 1: Shoe store: 30% off sneakers this weekend	Sent to many people: true; Sale or deal words: true; Unsubscribe link: true	Promotions tab
Email 2: Toy shop: today's deal on building kits	Sent to many people: true; Sale or deal words: true; Unsubscribe link: true	Promotions tab
Email 3: Your order has shipped	Sent to many people: false; Sale or deal words: false; Unsubscribe link: false	Another tab
Email 4: Grandpa: there is a sale at the bike shop, want to go?	Sent to many people: false; Sale or deal words: true; Unsubscribe link: false	Another tab
Email 5: School newsletter: field trip forms due	Sent to many people: true; Sale or deal words: false; Unsubscribe link: true	Another tab
Email 6: Library: your book is due Friday	Sent to many people: false; Sale or deal words: false; Unsubscribe link: false	Another tab

Test cases

Item	Values	Right move or bin
Email 7: Pizza place: two-for-one deal tonight	Sent to many people: true; Sale or deal words: true; Unsubscribe link: true	Promotions tab
Email 8: Music app: your weekly playlist is ready	Sent to many people: true; Sale or deal words: false; Unsubscribe link: true	Another tab
Email 9: School club: bake sale this Saturday	Sent to many people: true; Sale or deal words: true; Unsubscribe link: true	Another tab

Check it

How is email sorting different from a spam filter?

Answer: It picks a tab for wanted mail. A spam filter decides junk or not. Sorting picks one of several tabs for mail you do want.

Your rule put the school bake sale in Promotions. Why?

Answer: It has the same clues as an ad. It was sent to many people and says "sale", just like a store ad.

You move an email to a different tab. What can that do?

Answer: Give the sorter a new example. A move is a new labeled example the sorter can learn from.

For older readers

Email sorting is multi-class classification: each email gets exactly one label from several classes (inbox, promotions, updates). A spam filter is binary classification, with only two classes. One way to build a multi-class sorter is a set of binary questions, one per tab ("promotions or not?"), which is what the toy shows. The labels come from examples, including the moves people make.

Questions

Its clues, such as the sender or what it says, looked like an ad. Moving it back gives the sorter a new example.

No. Promotions are ads and newsletters you signed up for. Spam is junk or scams nobody asked for, and a spam filter handles it.

No. Some email apps sort mail into tabs and some do not, and the tab names can differ.