Best Open Source Alternatives to Fastmail

Compare the best free and open-source alternatives to Fastmail — self-hosted and desktop replacements you fully control, ranked by GitHub stars, license and platform support.

Curated by open-source.store · Updated August 2026 · 3 alternatives

Fastmail

Proprietary SaaS

PricingPaid

Platformsweb, ios, android

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Fastmail alternatives compared

Open-source alternatives to Fastmail, compared by stars, license and platform
Tool		License	Platforms	Self-hosted
Mail-in-a-Box	15,374	CC0-1.0	Linux	Yes	May 2026	Visit
Mailcow	13,205	GPL-3.0	LinuxDocker	Yes	Aug 2026	Visit
Roundcube	7,106	GPL-3.0	LinuxDocker	Yes	Jul 2026	Visit

Top open-source Fastmail alternatives

Mail-in-a-Box15,374CC0-1.0

Easy-to-setup self-hosted mail server.

Linux

vs Fastmail: a free, open-source option you fully control, licensed CC0-1.0.

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Mailcow13,205GPL-3.0

Modern self-hosted mailserver suite based on Docker.

LinuxDocker

vs Fastmail: a free, open-source option you fully control, licensed GPL-3.0.

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Roundcube7,106GPL-3.0

Browser-based multilingual IMAP client with an application-like user interface.

LinuxDocker

vs Fastmail: a free, open-source option you fully control, licensed GPL-3.0.

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