smtprelayd Self-Hosted SMTP Relay

Explore this developer service’s ongoing no-cost allowance, restrictions and official documentation before deploying.

INCLUDED FREE ALLOWANCEGPL-3.0-or-later self-hosted SMTP relay software for Windows and Linux with durable queue, SMTP submission, routing, OAuth2/XOAUTH2 Microsoft 365 smarthost integration, JSON API and metrics; no vendor software quota or expiry.

View official documentation

Plan details

What do these plan and deployment labels mean?

Plan: Ongoing free allowance
Deployment model: Self-hosted
Credit card: Not required
Commercial use: Allowed
Added to directory (UTC): 2026-11-09
Last checked: 2026-11-08

Important restrictions

Not a free mailbox or hosted email sending service. Requires your own Windows/Linux host, secure SMTP configuration and an existing smarthost (such as Microsoft 365) with separate licensing, sending limits and possible charges. Harden network access to avoid an open relay; upstream reports production use but deployment security remains operator responsibility.

View official documentation

Independent community listing, not affiliated with the provider. Always check the latest billing policy and quotas before enabling paid usage.