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OpenSMTPD review

Free#30 of 34 in Mail Server Software

A focused SMTP server for self-hosted mail routing, relay, and delivery.

6.2/10Editor score
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

OpenSMTPD is a free, open-source server-side SMTP implementation from the OpenBSD Project. It is designed for administrators running self-hosted mail infrastructure on OpenBSD, FreeBSD, NetBSD, DragonFlyBSD, Linux, SmartOS, or macOS. Its scope is focused: the software accepts, routes, relays, queues, and delivers email rather than presenting a complete mailbox experience for end users. That makes it a fit for SMTP infrastructure, relay services, backup-MX operation, and local delivery workflows.

Its strongest area is mail transport control. OpenSMTPD supports server-side SMTP message exchange, delivery scheduling, aliases, virtual-user mappings, TLS, authenticated SMTP sessions, LMTP, custom mail delivery agents, and local delivery to mbox and Maildir. The SMTP filtering API adds an extension point for filtering workflows, while privilege separation and chroot-based process isolation support a security-conscious server design. Administrators can therefore shape routing and delivery around their own Unix-based environment instead of adopting a broader hosted mailbox suite.

The free, open-source model keeps the product aligned with teams that want direct control over deployment and configuration. The trade-off is its narrow focus: webmail, IMAP/POP3 access, and mobile synchronization are outside the product's stated capabilities, and high availability is not part of its positioning. Choose OpenSMTPD when the requirement is a minimal SMTP relay or self-hosted mail transport layer. Choose another product when users need browser-based mail, mailbox access through standard retrieval protocols, mobile sync, or a broader collaboration-oriented email platform.

OpenSMTPD pros and cons

  • Where it wins
    • Handles SMTP exchange, relay, backup MX, queues, and local delivery
    • Supports TLS, authentication, aliases, virtual users, and filtering APIs
    • Uses privilege separation and chroot-based process isolation
  • Where it doesn't
    • Does not provide a webmail interface
    • Does not include IMAP or POP3 mailbox access
    • Lacks mobile synchronization and high availability

OpenSMTPD fact sheet, pricing and score →

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