Head-to-Head Comparison · Alternative to Fastmail · 📬 email
Fastmail vs Mailspring
A fast unified desktop inbox with local search; workflow extras still cost money. Here is how Mailspring ($0/mo open source) stacks up against Fastmail ($6/mo) across cost, hosting, data privacy, and real-world trade-offs.
Mailspring
$0.00/mo · GPL-3.0
Fastmail vs Mailspring Specification Matrix
facts verified 2026-08-10
| Dimension | Fastmail (Paid) | Mailspring (Replacement) |
|---|---|---|
| Monthly Price | $6 / mo | $0 / mo |
| 1-Year Cost (1 seat) | $72 / yr | $0 / yr (Save $72) |
| 1-Year Cost (5 seats) | $360 / yr | $0 / yr (Save $360) |
| 1-Year Cost (10 seats) | $720 / yr | $0 / yr (Save $720) |
| Source & License | Proprietary SaaS | open source GPL-3.0 |
| Where It Runs | Vendor Cloud | Local (on your machine) |
| Platforms | Web / Cloud | desktopone-click install |
| GitHub Stars | — | ★ 18k (active aug 2026) |
Deep Dive: Switching from Fastmail to Mailspring
Trade-offs, installation & data architecture
What you trade away
Mailspring is only a client, so it cannot replace Fastmail’s hosted mailbox, custom-domain delivery, aliases, server-side filtering, calendar, and contacts.
How to deploy Mailspring
Install the packaged desktop app for macOS, Windows, or Linux and create a Mailspring ID
What it takes to run
A Mailspring ID is mandatory, and there are no mobile clients
Where your data lives
Mail 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
Why fork Mailspring instead of vibe-coding a Fastmail clone?
A consolation build is possible, but the paid product's decisive value sits outside a solo rebuild. For Fastmail, build a clean client for an existing mailbox without running public mail infrastructure. The hard boundary is mail hosting, spam filtering, domains, calendars, contacts, deliverability, and support, plus mail infrastructure, integrations, and client polish.
Fastmail vs Mailspring FAQ
Is Mailspring a good free alternative to Fastmail?+
Yes. Mailspring is a verified open-source (GPL-3.0) replacement for Fastmail. A fast unified desktop inbox with local search; workflow extras still cost money.
What is the catch when switching from Fastmail to Mailspring?+
Mailspring is only a client, so it cannot replace Fastmail’s hosted mailbox, custom-domain delivery, aliases, server-side filtering, calendar, and contacts.
How much do you save switching from Fastmail to Mailspring?+
Fastmail costs $6/mo ($72/yr) per seat, whereas Mailspring is $0/mo. Switching saves $72/yr for a solo user, $360/yr for a 5-person team, and $720/yr for a 10-person team.
How do I install or self-host Mailspring instead of Fastmail?+
Install: Install the packaged desktop app for macOS, Windows, or Linux and create a Mailspring ID. Setup: A Mailspring ID is mandatory, and there are no mobile clients
