Fastmail alternatives: 4 open-source picks
Fastmail costs $6/mo — $72 a year. These 4 alternatives replace it for $0, led by Mailspring, Stalwart and Thunderbird. All 4 are open source. License, stars and last commit checked by hand on 2026-08-29. No trials, no crippled tiers.
A fast unified desktop inbox with local search; workflow extras still cost money.
licenseGPL-3.0
runson your machine
installInstall the packaged desktop app for macOS, Windows, or Linux and create a Mailspring ID
dataMail is synchronized and indexed into a local database and cache; Mailspring's service stores account and feature metadata but says it does not store message content except for features such as shared threads
the catch vs FastmailMailspring is only a client, so it cannot replace Fastmail’s hosted mailbox, custom-domain delivery, aliases, server-side filtering, calendar, and contacts.
setupA Mailspring ID is mandatory, and there are no mobile clients
facts verified 2026-08-10
Modern all-in-one mail server in Rust with JMAP, IMAP, and SMTP plus built-in spam filtering.
licenseAGPL-3.0
runsyour server
setupnot verified by us yet — check the repo README
facts verified 2026-08-29
A mature client for almost any mailbox; the interface has survived more redesign cycles than most startups.
licenseMPL-2.0
runson your machine
installInstall the official Windows, macOS, or Linux package and add existing mail accounts
dataAccounts, settings, indexes, address books, and locally downloaded messages live in the Thunderbird profile; message stores use mbox by default, with Maildir available, while IMAP originals remain at the provider
setup✓ installs clean
the catch vs FastmailThunderbird is only a client, so it cannot replace Fastmail’s hosted mailbox, custom-domain delivery, aliases, server-side filtering, calendar, and contacts.
facts verified 2026-08-10
High-performance single-binary newsletter and mailing list manager with campaigns, templates, and Postgres backend
licenseAGPL-3.0
runsyour server
setupnot verified by us yet — check the repo README
facts verified 2026-08-29
What each one is, in full: Stalwart · Listmonk
last updated 2026-08-29 · no votes, no pay-to-list · just what's real
how to choose a Fastmail alternative
Easiest to get running
Mailspring — a one-click install, no server to maintain.
Most proven
Listmonk, with 22,000 GitHub stars — the largest community of the 4, which usually means more answers when something breaks.
Runs on your own machine, no server
Mailspring — nothing to host, your data stays on your disk.
what you give up by leaving Fastmail
- mail hosting, spam filtering, domains, calendars, contacts, deliverability, and support
- mail hosting and deliverability
- push on every platform
- advanced team collaboration
- provider-specific AI and search
None of the picks above covers all of it. The full verdict says which gaps matter.
Fastmail alternatives at a glance
| tool | license | running it | platforms | stars | active |
|---|---|---|---|---|---|
| Mailspring | GPL-3.0 | one-click install | macos, windows, linux | 17,724 | 2026-08 |
| Stalwart | AGPL-3.0 | docker to self-host | self-hosted, web | 8,000 | 2026-08 |
| Thunderbird | MPL-2.0 | one-click install | macos, windows, linux | 92 | 2026-08 |
| Listmonk | AGPL-3.0 | one-click install | self-hosted, web | 22,000 | 2026-08 |
why people still pay for Fastmail
People still pay for Fastmail because an email client can be rebuilt; operating a trusted mail service with excellent deliverability cannot. The recurring cost buys IMAP quirks, OAuth, MIME, threading, search, attachments, offline sync, notifications, secure storage, and provider changes, not just the visible interface. If none of that applies to you, any pick above saves $72 a year.
questions about switching from Fastmail
Is there an open-source alternative to Fastmail?
Yes: Mailspring, Stalwart, Thunderbird and 1 more. Every tool on this page is open source: no trials, no crippled tiers.
Can open source really replace Fastmail?
Our verdict is YES. Listmonk (22k stars), Mailspring (18k stars), Stalwart (8k stars) are mature open-source replacements for Fastmail — self-host in one command and stop paying $6/mo. The full verdict, and what you give up by switching, is at caniopensourceit.online/fastmail.
What is the easiest open-source Fastmail alternative to set up?
Mailspring — a one-click install, no server to maintain.
What is the most popular open-source Fastmail alternative?
By GitHub stars, Listmonk (22,000). Mailspring is next with 17,724.
