OpenSMTPD review
A free, self-hosted SMTP relay and router for administrators—not a mailbox server.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
OpenSMTPD is an open-source mail transfer agent maintained by the OpenBSD Project. It is intended for administrators who need to accept, queue, route, relay, or locally deliver email, rather than provide end users with mailbox access. It can accept SMTP connections over network interfaces or a local Unix socket, then route messages to another SMTP server or deliver them locally through mbox, Maildir, LMTP, or an external mail delivery agent. It runs on OpenBSD, FreeBSD, Linux, and macOS, with self-hosted deployment.
Its scope is focused on mail transfer and routing. Administrators can configure rules, aliases, virtual address expansion, and user lookups, as well as authenticated SMTP submission and TLS or SMTPS listeners. Messages can be relayed to authenticated and TLS-protected SMTP servers; configurable external filters and filter chains can be part of the routing flow. Queueing supports later delivery or relay, and the server can be configured for backup MX behavior and message queue expiration. This makes OpenSMTPD a fit for mail infrastructure where control over routing and delivery matters, but not a replacement for a complete email service.
OpenSMTPD is free and open source, with community support and self-hosted operation. Its supported protocols are SMTP and LMTP; it is an MTA, not a mailbox server, so teams needing user-facing mailbox retrieval or webmail should choose a separate product for that role. The trade-off is operational responsibility: administrators must manage the server and its configuration themselves. Choose OpenSMTPD for a lightweight transfer and routing component, including relay or local delivery needs; look elsewhere if the requirement is an integrated mail platform with mailboxes.
OpenSMTPD pros and cons
- Where it wins
- Queues accepted messages for later delivery or relay.
- Routes mail through rules, aliases, virtual addresses, and user lookups.
- Supports TLS, authenticated submission, filtering, and backup MX behavior.
- Where it doesn't
- Does not provide mailbox storage or webmail.
- Supported protocols are limited to SMTP and LMTP.
- Requires administrators to operate and configure self-hosted mail infrastructure.
OpenSMTPD fact sheet, pricing and score →
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