How We Handle Emails
A deeply engineered architecture designed for extreme performance, rigorous security, and uncompromising privacy. Every message is processed through a robust, multi-stage pipeline.
Architecture Overview
Shared Frontend UI
Our Next.js frontend intelligently routes actions to totally distinct backends depending on the domain. Core mail reading and sending happen via the Express API, while real-time incoming mail alerts are continuously streamed through the parallel Socket.IO connection. Modern features like Workspace collaboration, Calendar syncing, and IMAP bridges hit our ultra-fast Go Microservices.
The Worker & MTA Layer
When you send an email, Express drops a job into the BullMQ/Redis Queues. The background workers pick it up, format the email, apply tracking/PGP, and hand it to our Custom MTA for outbound routing across ports 25 and 587. When the MTA receives a delivery receipt, it drops a message via Redis Pub/Sub back up to Socket.IO, which alerts your browser UI.
Scalable Edge Nodes
Dedicated Stage 0 SMTP listeners for fast acceptance (<200ms) with mid-stream back-pressure. Our resilient outbound nodes use a custom Go-built MTA ensuring advanced TCP pooling, retries, and comprehensive DSN generation.
High-Speed Queues
Messages seamlessly enter a Redis-backed multi-stage worker pipeline, handling intense workloads through distributed streams without blocking vital SMTP connections.
Secure At-Rest Storage
High-speed PostgreSQL stores account metadata, attachments sit in S3-compatible endpoints, while the mail payloads themselves are safeguarded by dual-layer AES and PGP encryption.
The Inbound Pipeline
Incoming emails pass through four stringent, specialized stages to guarantee fast routing, accurate spam detection, and protocol compliance.
0Edge Acceptance Layer
- Instant Blacklist Check: Redis & DNS Spamhaus RBL lookups drop attacks immediately.
- Bounce Envelope Detection: Instant VERP recognition limits processing overhead.
- Early Rejection: System accounts (noreply/postmaster) are protected before bodies are parsed.
- Quota Guard & Size Limits: Checks usage capacities instantly and enforces explicit max message sizes mid-stream.
1Anti-Spam & Authentication
- Duplicate Prevention: Advanced SHA-256 fingerprinting drops spam bursts entirely.
- Parallel Verification: PTR, MX, SPF, DKIM, and DMARC evaluated synchronously.
- TOML-Driven Scoring engine: Uses DNSBL APIs, OpenPhish, and rule-based DSL logic.
- Sieve Filter Engine: Enforces JSON-based rule sets dynamically sorting into folders.
- ARC Sealing: Applies comprehensive ARC cryptographic signatures maintaining chain of custody.
2Delivery & Real-Time Sync
- Privacy Stripping: Intercepts and blocks tracking pixels and URL parameters.
- Smart Threading: Deep header analysis groups conversations intelligently.
- Automatic Responders: Distinct queues handle looping, auto-replies, and vacation behaviors.
- Real-time Dispatches: Socket.IO & Redis Pub/Sub fire inbound notifications instantly.
3Bounce DSN Management
- RFC 3464 Compliance: Standardized multi-part human/machine delivery status generation.
- Parameter Support: Respects extensive DSN preferences like RET=FULL/HDRS and NOTIFY logic.
- Smart Classification: Seamlessly differentiates between 4xx and 5xx errors translating to user-friendly messages.
The Outbound Pipeline
Submission & Rate Limiting
Secure Port 587 handoffs utilizing PLAIN, LOGIN, and XOAUTH2. Tiered per-user rate limits (minute/hour/day) and robust quota verification.
API Submission & Multi-Provider Bridge
Full REST API dispatch capability with smart failover strategies wrapping numerous providers (Sendgrid, Resend, etc.) or our custom MTA.
DKIM & Cryptography
Dynamically signs payloads at the application level ensuring zero-trust. Sent duplicates are similarly backed by PGP at-rest encryption within your secure sent folder.
Automated DNS Management
Automatically scaffolds optimal SPF, DKIM, DMARC, MX, MTA-STS, and Autodiscover records enabling fully compliant domain onboarding.
Privacy & Anti-Spam Protection
Tracking Protection
Proactively strips 1x1 pixels and intrusive parameters like utm_* or fbclid. We operate a highly scalable Image Proxy Server that scrubs referrers and ensures zero data leaks when opening messages.
Multi-vector Spam Defense
Leverages multi-layer heuristic evaluations spanning continuous OpenPhish indexing, disposable-domain trapping, IPv6 zone resolution, and explicit attachment classification algorithms.
At-Rest PGP
Messages are isolated and sealed cryptographically before permanent disk allocation.
- Dual-layer: OpenPGP encrypt + Database AES wrapping.
- Argon2id key derivation securely caches private components.
- SRS implementations strictly isolate redirected chains.
Event & Webhooks
Integrate smoothly into backend infrastructure through exhaustive system dispatches.
- Publishes rich payloads covering Delivery, Bounce, Rejection, and Failures.
- Secured strictly via HMAC-SHA256 authenticated signatures.
- Real-time connection bridging streams direct into frontend sockets.
Routine Telemetry
Persistent, resilient background workers ensure zero maintenance degradation.
- Automatically purges orphaned multi-part objects and abandoned caches.
- ICS calendar consumer seamlessly parses incoming RSVP requests.
- MTA-STS adherence validates strict transport layer securities.