Cyrus IMAP vs Exim
A side-by-side comparison of two self-hosted mail servers options — licensing, setup difficulty, resource needs, and what each one replaces.
| Feature | Cyrus IMAP | Exim |
|---|---|---|
| Deploy effort | Read-the-docs project | Read-the-docs project |
| Health score | 80 · Excellent | 15 · At risk |
| Status | Actively maintained | Archived |
| Category | Mail Servers | Mail Servers |
| License | BSD-3-Clause | GPL-2.0 |
| Language | C | C |
| Setup difficulty | Hard | Hard |
| Min. RAM | 1,024 MB | 64 MB |
| Deployment | bare-metal, source | bare-metal, source |
| GitHub stars | ★ 648 | ★ 785 |
| First released | 1994 | 1995 |
| Replaces | Microsoft Exchange | Microsoft Exchange |
What are Cyrus IMAP and Exim?
Cyrus IMAP
Cyrus IMAP is an enterprise-grade mail server designed to scale to very large numbers of mailboxes, with its own optimized mail store. It supports IMAP, POP, JMAP, and server-side search.
- Scales to many mailboxes
- Optimized mail store
- JMAP and IMAP support
- Server-side search
Exim
Exim is a highly configurable mail transfer agent used to route and deliver email on Unix systems. It powers a large share of the internet's mail servers and supports extensive policy and ACL controls.
- Powerful routing rules
- ACL-based policy
- Wide platform support
- Mature codebase
Cyrus IMAP vs Exim: key differences
The biggest difference is maintenance: Exim's repository is archived and no longer developed, while Cyrus IMAP is actively maintained. Both projects are written in C. Licensing differs — BSD-3-Clause for Cyrus IMAP versus GPL-2.0 for Exim. Exim is the lighter option, starting around 64 MB of RAM against 1,024 MB for Cyrus IMAP.
Why pick each one
Choose Exim if…
- Extremely flexible
- Proven at scale
Watch out for
- Complex configuration
- Easy to misconfigure
Frequently asked questions
Is Cyrus IMAP or Exim better?
Neither is universally better. Exim has the larger community; both share a hard setup difficulty, so the decision comes down to features and licensing.
Are Cyrus IMAP and Exim free and open-source?
Yes. Cyrus IMAP is licensed under BSD-3-Clause and Exim under GPL-2.0. Both can be self-hosted at no software cost.
Can I run Cyrus IMAP and Exim with Docker?
Cyrus IMAP: check the project docs for container support. Exim: check the project docs for container support.
Which is lighter on resources, Cyrus IMAP or Exim?
Exim has the smaller minimum footprint at 64 MB of RAM, compared to about 1,024 MB for Cyrus IMAP. Real-world usage depends on library size, user count, and enabled features.