Glassmail vs Thunderbird on Mac: free and open vs native
Thunderbird is free, open source and endlessly configurable. Glassmail is a native Mac app with private AI built in. How to choose between them.
Short answer: choose Thunderbird if you want free, open-source software, run Windows or Linux too, or like extending your mail client with add-ons. Choose Glassmail if you want an app that feels made for the Mac, does the sorting for you, and has an AI assistant that runs on your Mac, for a one-time price.
Both talk directly to your email provider, and neither has a company server reading your mail.
At a glance
| Glassmail | Thunderbird | |
|---|---|---|
| Price | $49 once (lower launch prices for early buyers) | Free, donation-supported |
| Open source | No | Yes |
| Platforms | Mac (macOS 14+) | Mac, Windows, Linux, Android |
| Feel on macOS | Native, built in Swift | Cross-platform interface |
| Accounts | Gmail, iCloud, Outlook, Microsoft 365, Yahoo, Fastmail, any IMAP | Gmail, Outlook, Yahoo, iCloud, IMAP, POP |
| Calendar | Adds dates from mail to Apple Calendar | Built in |
| Built-in AI | Assistant, summaries, writer, on your Mac | None; via add-ons |
| Sorting | People first, updates bundled by sender | Folders, filters and tags you set up |
Disclosure: Glassmail is our app. Tell us at hi@glassmail.app if anything here is wrong.
Thunderbird’s strengths
It’s free, open source and backed by a non-profit. It runs everywhere, includes a calendar, supports POP as well as IMAP, and its add-on library lets you build almost any workflow. If you want to own and inspect your tools, it’s the obvious pick.
Glassmail’s strengths
Glassmail is made only for the Mac, so it follows macOS conventions and stays fast with years of mail. It does work for you that Thunderbird leaves to filters: mail from people separated from updates, sign-in codes with a copy button, a Today view of who’s waiting on you, and one-key Triage. Its assistant answers “what needs me today?” and drafts replies in your voice using Apple Intelligence or a small downloaded model, entirely on your Mac. More on private AI for email.
Which should you choose?
- Choose Thunderbird if free and open source matter most, you use several operating systems, or you want a calendar and add-ons.
- Choose Glassmail if you’re on a Mac and want a native app that sorts and summarises for you, privately, for one payment.
Glassmail is free for 14 days. More options: the best Apple Mail alternatives.
Quick answers
Is Thunderbird good on a Mac?
Thunderbird works well on a Mac and is free and open source, with add-ons for almost anything. It's the same app as on Windows and Linux, so it doesn't look or behave like a native Mac app.
Does Thunderbird have AI features?
Not built into the free desktop app as of late 2026. Add-ons can connect it to AI services, and Mozilla has talked about an optional assistant for its paid Thunderbird Pro services. Glassmail includes an AI assistant, summaries and a writer that run on your Mac.
Is Glassmail open source like Thunderbird?
No. Glassmail is a paid, closed-source app made by one independent developer. It has no mail server, keeps your mail on your Mac, and its privacy policy lists every connection the app makes.