Both are free, both are open source, and both put mail, calendar and contacts on your Mac, Windows or Linux computer. They are built for different people. We made CitrusMail, so we will tell you where Thunderbird is the better pick, too.
Side by side
| CitrusMail | Thunderbird | |
|---|---|---|
| Price | Free | Free, funded by donations |
| Code | MIT | Open source |
| Computers | Mac, Windows, Linux | Mac, Windows, Linux, older Windows too |
| Phone | No | Android app |
| Calendar and contacts | Yes, CalDAV and CardDAV | Yes, plus tasks |
| Several mailboxes | Yes, with a switcher | Yes, with a unified inbox |
| Read receipts | Built in: Delivered, Opened, Bounced | Not on its feature page |
| AI help | Your own key: summaries, replies, questions | Not on its feature page |
| Translation | Both ways, with your AI key | Not on its feature page |
| Add-ons | No | Large catalogue |
| Your own name on it | Yes, brand and build your own app | No |
| Age | Version 0.1.0 | Over 20 years |
Where Thunderbird wins
Maturity, first. Thunderbird has been worked on for more than 20 years, and it shows in how much it can do. Its add-on catalogue covers needs we have not thought of, it has tasks next to the calendar, and its unified inbox puts every account in one list. It also has an Android app, and builds for 32-bit systems and Windows 7 and 8.1.
If you run many accounts in one list, depend on a particular add-on, or want mail on your phone from the same project, Thunderbird is the right choice today.
Where CitrusMail wins
CitrusMail is built for the person who wants it to work well without a settings tour. You type your email and password; it finds the servers. Mail, calendar and contacts share one clean window, with keyboard shortcuts for everything (press ? to see them).
The features people install add-ons for are already there. Track a message and Sent shows Delivered, Opened or Bounced. Add a key from Anthropic, OpenAI, Google, xAI or Perplexity and you get summaries of long messages, AI Reply, questions across every folder and translation both ways, from the model you already pay for. Each mailbox gets its own signature, written in the app or pasted as HTML. Send later, rules and one-click unsubscribe are in too.
And because the code is MIT and built to be rebranded, a company can put its own name, logo and mail servers on it and give staff an app that only asks for an email and a password.
A note on read receipts
CitrusMail tracks opens three ways: the standard receipt request, a delivery report from your server, and a small tracking image. The image needs somewhere public to live. For Faivelo mailboxes, Faivelo serves it, so it works straight from the desktop app. With other providers, it works once CitrusMail is hosted at its own web address. Tracking is off until you set it up, and you choose it per message.
Which should you use?
- Pick CitrusMail if. you want a modern all-in-one window, read receipts and AI without add-ons, or an app you can brand for your team. Get it here.
- Pick Thunderbird if. you need add-ons, tasks, a unified inbox or an Android app from the same project.
They do not fight over your mail: both read the same IMAP mailbox, so you can run them side by side for a week and keep the one you open more. For the wider field, see the best open source email clients, compared.
FAQs
Is CitrusMail a Thunderbird fork?
No. CitrusMail is its own app, built with Nuxt and Electron. It uses Thunderbird's public database of mail server settings to find yours when you sign in.
Can I use CitrusMail and Thunderbird at the same time?
Yes. Both read your mail over IMAP, so the same messages and folders show in each.
Does CitrusMail have a unified inbox?
Not yet. You can add several mailboxes and switch between them with Ctrl+2, 3 and 4.
Is CitrusMail free?
Yes. The app is free and the code is MIT licensed. AI features use your own key, so the model provider bills you for what you use.
Give CitrusMail a week
It is free, and it reads the same mailbox Thunderbird does, so you lose nothing by trying it next to it.
- Read receipts built in
- Your own AI key
- Mac, Windows and Linux