Medium · 12 steps · ~70 min

Design an email service

Send, receive, search, and never lose a message.

People search mailboxes constantly and expect every message to be stored safely. Incoming mail arrives in bursts.

Same problem as GmailOutlookProton Mail

How it works

• Receive: accept mail fast, store it, index it for search.
• Search: query an index instead of scanning every message.

What you'll build

1. The API and the data behind it
2. A server, a database and a search index
3. A queue and workers that absorb a newsletter burst
4. A rate limiter against a spam flood
5. A design that survives a cold cache, a lost index node and a lost primary

Steps

1. 1Design the API
2. 2Design the data model
3. 3Handle 500 requests/sec
4. 4Handle 5,000 requests/sec for $1,000 a month
5. 5Handle 25,000 requests/sec
6. 6Absorb a 50,000 requests/sec mail burst
7. 7Survive a spam flood on a budget
8. 8Survive a cache restart
9. 9Lose a search node
10. 10Lose the primary database
11. 11Mail is missing from search
12. 12Deep dive: duplicate deliveries