What is the difference between Fastmail and Stalwart?

Fastmail: Paid, ad-free email hosting with calendars, contacts, custom domains and masked email addresses, built on open standards (IMAP, JMAP, CalDAV). Stalwart: A Rust mail and collaboration server that handles SMTP, IMAP, POP3 and JMAP, plus CalDAV, CardDAV and WebDAV, with built-in spam filtering, DKIM, DMARC and a web admin.

When should I choose Fastmail?

An individual, family or small business wants fast, private email on its own domain without Google or Microsoft.

When should I choose Stalwart?

You want to self-host email, calendars and contacts in one modern binary instead of assembling Postfix, Dovecot and Rspamd.

Fastmail vs Stalwart

Fastmail and Stalwart are both email server software. Fastmail is a commercial product from Fastmail Pty Ltd. Stalwart is open source under a license set out in its repository, with 16k GitHub stars.

Which to pick

Pick Fastmail when: An individual, family or small business wants fast, private email on its own domain without Google or Microsoft.
Pick Stalwart when: You want to self-host email, calendars and contacts in one modern binary instead of assembling Postfix, Dovecot and Rspamd.

Side by side

Fastmail Stalwart

What it does

Paid, ad-free email hosting with calendars, contacts, custom domains and masked email addresses, built on open standards (IMAP, JMAP, CalDAV).

A Rust mail and collaboration server that handles SMTP, IMAP, POP3 and JMAP, plus CalDAV, CardDAV and WebDAV, with built-in spam filtering, DKIM, DMARC and a web admin.

Watch out

No office suite or file storage included, and data is held in Australia and the US.

Some features are reserved for the paid Enterprise edition, it only recently reached 1.0, and running any mail server means owning deliverability.

Ready for

Production-ready

Usable

Runs as

Cloud service and mobile app

Self-hosted server

Built with

Not published

Rust, RocksDB and PostgreSQL

Source code

Closed source, sold by Fastmail Pty Ltd

Open source, license unclear on GitHub

What the license allows

Closed source: you use it under the maker's terms and cannot change or resell the code.

GitHub could not read the license. Check it in the repository before reusing any code.

How widely known

586 Wikipedia readers a month on phones

16k GitHub stars

How established

Not known

Established: started 3 years ago, latest release v1.0.3.

Other comparisons

Fastmail vs Gmail (Google Workspace)Gmail (Google Workspace) vs Stalwart Fastmail vs Proton Mail Proton Mail vs Stalwart Docker Mailserver vs Fastmail Fastmail vs Mail-in-a-Box Docker Mailserver vs Stalwart Mail-in-a-Box vs Stalwart

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Every email server product and project, ranked

Both sides were judged on 2026-11-03 from makers' descriptions, Wikipedia, READMEs and GitHub data. License, age and popularity lines are worked out directly.