Nullmailer vs OpenSMTPD
A side-by-side comparison of two self-hosted mail servers options — licensing, setup difficulty, resource needs, and what each one replaces.
| Feature | Nullmailer | OpenSMTPD |
|---|---|---|
| Deploy effort | Read-the-docs project | Read-the-docs project |
| Health score | 8 · At risk | 80 · Excellent |
| Category | Mail Servers | Mail Servers |
| License | GPL-2.0 | ISC |
| Language | C++ | C |
| Setup difficulty | Easy | Medium |
| Min. RAM | 16 MB | 32 MB |
| Deployment | bare-metal, source | bare-metal, source |
| GitHub stars | ★ 199 | ★ 586 |
| First released | 2000 | 2013 |
| Replaces | Sendmail | Sendmail, Postfix |
What are Nullmailer and OpenSMTPD?
Nullmailer
Nullmailer is a minimal mail transfer agent designed only to relay outgoing mail to a smart host. It is ideal for servers and workstations that need to send notifications without running a full MTA.
- Relay-only operation
- Tiny footprint
- Smart host forwarding
- Queue management
OpenSMTPD
OpenSMTPD is a free implementation of the SMTP protocol developed by the OpenBSD project. It emphasizes simplicity, security, and a readable configuration syntax for running your own mail relay or server.
- Simple configuration
- Security focused
- SMTP relay and delivery
- Filters via extensions
Nullmailer vs OpenSMTPD: key differences
Nullmailer is written in C++, while OpenSMTPD is built with C. Licensing differs — GPL-2.0 for Nullmailer versus ISC for OpenSMTPD. Nullmailer is the lighter option, starting around 16 MB of RAM against 32 MB for OpenSMTPD. Nullmailer is the more established project (first released 2000), while OpenSMTPD arrived in 2013. OpenSMTPD has the considerably larger community, at 586 GitHub stars versus 199.
Why pick each one
Choose Nullmailer if…
- Extremely lightweight
- Simple configuration
Watch out for
- Cannot receive mail
- No local delivery
Choose OpenSMTPD if…
- Clean concise config
- Strong security record
Watch out for
- Fewer features than Postfix
- Smaller ecosystem
Frequently asked questions
Is Nullmailer or OpenSMTPD better?
Neither is universally better. OpenSMTPD has the larger community, while Nullmailer is simpler to set up (easy difficulty). Choose based on the comparison table above and your own setup.
Are Nullmailer and OpenSMTPD free and open-source?
Yes. Nullmailer is licensed under GPL-2.0 and OpenSMTPD under ISC. Both can be self-hosted at no software cost.
Can I run Nullmailer and OpenSMTPD with Docker?
Nullmailer: check the project docs for container support. OpenSMTPD: check the project docs for container support.
Which is lighter on resources, Nullmailer or OpenSMTPD?
Nullmailer has the smaller minimum footprint at 16 MB of RAM, compared to about 32 MB for OpenSMTPD. Real-world usage depends on library size, user count, and enabled features.