Postal

Postal is a self-hosted mail delivery platform for transactional email: password resets, order confirmations, notifications, all on infrastructure you own instead of paying per email through SendGrid. You run your own email server, control your sending reputation, and pay nothing per message.

MIT license, Ruby. Full-featured: SMTP server, HTTP API, webhook delivery tracking, click/open tracking, bounce handling, multiple organizations and mail servers, IP pool management. Web UI included for monitoring and configuration.

Fully free to self-host. No paid tier. Your costs are infrastructure: a VPS ($10-20/mo), a dedicated IP with clean reputation, and the time to set up DNS records (SPF, DKIM, DMARC). Solo developers sending a few hundred emails/month: overkill. Use Resend's free tier. Small teams sending thousands/month: Postal starts making financial sense when you'd otherwise spend $50-100/mo on an ESP. Medium to large orgs sending 100K+/month: Postal pays for itself quickly: at $0.001/email on SendGrid, 100K emails is $100/mo. Postal costs you a $20 VPS.

The catch: email deliverability is hard. Running your own mail server means YOU are responsible for IP reputation, authentication records, warming up IPs, handling bounces correctly, and staying off blacklists. Get any of it wrong and your emails land in spam. This is not a 'set and forget' system. Budget 4-8 hours/month of ops minimum.