←SYSTEM DESIGNDesign an Email Service (Gmail)GoogleMicrosoftProton
TRAFFIC LEVEL—/3
CONSTRAINTS
Active users1B
Emails sent/day300B
Avg email size75 KB
Peak ingest rate1M emails/sec
Storage per user15 GB free
Compute & Network
Load BalancerDistribute traffic
API GatewayEntry point / auth
API ServerBusiness logic
Worker NodeAsync processing
CDN EdgeGlobal cache
WebSocket GatewayPersistent connections
Data Stores
PostgreSQLRelational DB
MySQLRelational DB
CassandraWide-Column DB
DynamoDBNoSQL / Managed
S3 BucketObject storage
Queues & Cache
Redis CacheIn-memory store
KafkaEvent stream
ZookeeperCoordination
Specialized
Bloom FilterProbabilistic set
Rate LimiterThrottling
Geohash ServiceGeospatial index
Trie ServerPrefix search
APNS / FCMPush notifications
AggregatorBatch / roll-up
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🚨 INCIDENT
GoogleMicrosoftProton
Design a large-scale email service supporting 1B+ users. Support sending, receiving, threading, search across 15 years of email history, spam filtering, and storage for users with 50GB+ of email. Handle 1M emails/second at peak (spam storms).