Design your own Gmail

Advanced55 minBuilds Email Inbox Synchronization ServiceRead first: 10.2 Delivery guarantees and idempotent consumers, 14.1 The inverted index, 13.1 Object storage

STEP 1 OF 13

The brief

You are designing an email service. Other mail servers deliver messages to your users over SMTP; your users read, search, label and send mail from web and phone apps. One rule outranks every other: once you accept a message, you never lose it.

How big it is

Users: about 1 billion
Inbound messages accepted: 8,000 requests / second
Mailbox reads (lists, threads, messages): 30,000 / second
Average message: about 50 KB, most of it attachments
p99 goal for reads: under 250 ms

What makes it tricky

Accepting is a promise. SMTP lets the sender retry until you say "250 OK"; after that, the message is your responsibility.
Most mail needs work before it is shown. Spam and virus scanning take time and must not block the sender.
Mailboxes are personal. Nothing is shared between users, which makes partitioning easy and caching at the edge useless.
Search must be fast but can be a little behind. A message that appears in search a few seconds after it arrives is fine; a message that is lost is not.

All changes saved

0 components · 0 connections

A blank canvas. A better system.

Add components from the palette, then drag between them to connect the request and event flow.

React Flow

Design your own Gmail

Advanced55 minBuilds Email Inbox Synchronization ServiceRead first: 10.2 Delivery guarantees and idempotent consumers, 14.1 The inverted index, 13.1 Object storage

STEP 1 OF 13

The brief

How big it is

Users: about 1 billion
Inbound messages accepted: 8,000 requests / second
Mailbox reads (lists, threads, messages): 30,000 / second
Average message: about 50 KB, most of it attachments
p99 goal for reads: under 250 ms

What makes it tricky

Accepting is a promise. SMTP lets the sender retry until you say "250 OK"; after that, the message is your responsibility.
Most mail needs work before it is shown. Spam and virus scanning take time and must not block the sender.
Mailboxes are personal. Nothing is shared between users, which makes partitioning easy and caching at the edge useless.
Search must be fast but can be a little behind. A message that appears in search a few seconds after it arrives is fine; a message that is lost is not.

All changes saved

0 components · 0 connections

A blank canvas. A better system.

Add components from the palette, then drag between them to connect the request and event flow.

React Flow