Updated May 1, 2026

Mailbird is a Windows desktop with a Mac build. Epistles is everywhere your inbox already lives.

Mailbird and Epistles both promise one window for every email account you keep. The questions that decide between them are which devices you read on, what you want the client to talk to your provider about, and how much of a Slack-and-Asana hub you want stapled to the side of your inbox. Here is the picture.

What Mailbird does well

Mailbird shipped on Windows in 2013 and has been the multi-account choice for Outlook-and-Gmail Windows users for most of a decade. The unified inbox works, the keyboard shortcuts are well thought through, the visual design has aged gracefully, and the team has earned the 4.5 million users their site claims. For someone whose primary machine is a Windows desktop and whose mail is scattered across Gmail, Outlook, iCloud, and a handful of IMAP hosts, Mailbird is a fair recommendation today.

The other thing Mailbird leans into is the integrations bundle. Slack, WhatsApp, Asana, Trello, Google Calendar, Dropbox, Instagram, and roughly thirty other services slide into a sidebar inside the mail window. If you genuinely want Slack and email in the same chrome, sharing one set of keyboard shortcuts and one notification surface, Mailbird has built for that and it works.

Pricing is straightforward. Free for one account, $4.03 a month billed yearly for unlimited accounts and the integration bundle, or a $99.75 lifetime license on sale from a $399 list. A Mac build was added later and shares the licence. No subscription gymnastics, no per-seat creep at the personal tier.

Where Mailbird stops

Mailbird is a desktop application, full stop. There is no iOS app, no Android app, no Linux build, and no web client. The Mac build exists; the team's own pricing page states plainly that mobile applications are on the roadmap and that Mailbird for Mac is not compatible with iPads or iPhones. If you read mail on a phone, and most of us do, Mailbird does not come with you.

Underneath, the connection story is mostly IMAP plus generic SMTP. Gmail, Outlook.com, iCloud, Yahoo, Exchange, Fastmail, and the rest are reached through the same generic IMAP pipe. That is a defensible engineering choice, it covers everyone, but it also flattens out the things each provider does well. Gmail's labels become folders, Microsoft's calendar invitations lose some of their structure, JMAP's push and Fastmail's mailbox semantics never get spoken in their own dialect. The integrations bundle is broad; the protocol depth is not.

ProtonMail is not supported without running Proton's Bridge, which is its own separate desktop process that has to stay running for IMAP to work, on a machine that is awake. That is not Mailbird's fault, it is Proton's design, but it is the practical experience.

What Epistles ships that Mailbird does not

Linux, iOS, Android, and Mac, today. Epistles runs on macOS, ships signed APT, DNF, and Flatpak repos at repo.epistles.com, all from the same codebase, and the iOS and Android builds are in early access. Windows and a browser app at app.epistles.com are in development with honest "coming" badges. The same accounts, the same shortcuts, the same local cache, on whichever device is in your hand.

Native protocols, not the IMAP lowest common denominator. Gmail through the Gmail API, Microsoft 365 through MS Graph, Fastmail through JMAP, ProtonMail through Proton's API with OpenPGP decryption on device, and anything else over IMAP and SMTP. Each adapter loads independently, so a Fastmail-only mailbox never downloads Gmail code, and a Gmail-only mailbox never downloads Proton's crypto. Labels stay labels, threads stay threads, push is push.

ProtonMail without Bridge. The Proton adapter speaks the API directly and decrypts your messages locally with OpenPGP.js. No second process, no IMAP shim, no requirement that another piece of software stay open in the background.

A zero-knowledge Cloud Vault. The credentials for every account you connect, OAuth refresh tokens, JMAP session blobs, IMAP passwords, are wrapped on your device with a key derived from your Epistles password and stored on our servers as opaque ciphertext bytes we cannot decrypt. Sign in on a second laptop or a new phone, type your password once, and your inboxes are already there. Proton is carved out: its mailbox passphrase and OpenPGP material live in your OS keychain only and never travel through the vault, by design.

No app-integration bloat. Epistles does one thing. Email, with calendar and contacts in the same window when you want them through CalDAV, CardDAV, JMAP, Google, and Microsoft. There is no Slack pane, no Trello pane, no Asana pane. If you want those tools, run those tools. If you want a mail client that is a mail client, this is one.

Zero telemetry. No analytics SDK, no crash-reporting SDK, no metrics pipeline. The only network calls Epistles makes to our servers are functional, your Cloud Vault, your account directory, and the future push relay. No silent observation of how long you hover on a subject line.

Open-source intent. The working tree is migrating to github.com/epistlesapp/epistles. Every claim on this page maps to code you can read.

Where Mailbird wins

A Windows native build, today. If you live on Windows as your primary mail surface, Mailbird is a serious answer and Epistles is not, yet. Our Windows build is in development and we will not pretend otherwise. Anyone telling you to switch to Epistles from a Windows-only workflow this week is selling you something.

The integrations bundle is the other place Mailbird earns its keep. If having Slack, WhatsApp, Asana, and your task manager docked into the mail window is genuinely how you want to work, Epistles deliberately does not do that. We think email is a job worth doing on its own, and we made a different bet. Yours might be the right one for you.

Maturity counts too. Mailbird has been in market since 2013. We are younger, and there are surface details, edge providers, esoteric IMAP servers, twenty-year-old folder hierarchies, where their years will tell against our months. If you find one of those, we want to hear about it.

The matrix, plainly

Platforms shipping today: Mailbird: Windows, macOS. Epistles: macOS, Linux, iOS, Android. (Epistles Windows and web in development. Mailbird mobile on roadmap.)
Email providers: Mailbird: any IMAP/SMTP host (Gmail, Outlook, iCloud, Yahoo, Exchange, Fastmail, etc.) over generic IMAP. Epistles: Gmail (Gmail API), Microsoft 365 (MS Graph), Fastmail (JMAP), ProtonMail (Proton API + OpenPGP), and IMAP/SMTP for the rest.
ProtonMail support: Mailbird: only via Proton's separate Bridge process. Epistles: native, no Bridge.
Cross-device account sync: Mailbird: per-device account setup. Epistles: zero-knowledge Cloud Vault carries connected-account credentials between devices, encrypted under your Epistles password.
App integrations (Slack, Asana, Trello, etc.): Mailbird: bundled, around 30 integrations docked in the mail window. Epistles: deliberately none. Email, calendar, contacts, that is the surface.
Pricing: Mailbird: free for 1 account; Premium $4.03/mo billed yearly for unlimited; lifetime $99.75 on sale ($399 list). Epistles: free for 3 accounts; $35/yr Pro for unlimited; 15-day trial, no card up front.
Telemetry: Mailbird: standard analytics and tracking present. Epistles: zero analytics SDKs, zero crash-reporting SDKs, zero metrics pipeline. Only functional API calls.
Open source: Mailbird: closed. Epistles: source migrating to a public repo at github.com/epistlesapp/epistles.

Who should pick which

If your primary device is a Windows desktop, your mail is mostly Gmail and Outlook over IMAP, and you want Slack and your task manager docked in the same window, Mailbird is a credible choice and we will not pretend otherwise. The integrations bundle is the wedge, and it is a real one for a real shape of working day. Pay for it.

If your inbox includes a Fastmail account that has outlasted three jobs, a ProtonMail you would rather not run a Bridge process for, a Microsoft 365 mailbox you would like to reach over MS Graph rather than flattened IMAP, or if you read mail on Linux, on an iPhone, or on an Android, then Mailbird cannot help and Epistles can. The native-protocols and cross-platform story is the wedge on this side of the page.

If the absence of telemetry, the zero-knowledge Cloud Vault, and an open-source working tree matter to you on principle, that is a third reason, and it stands on its own.

If you are still looking

Mailbird is a careful Windows email client with a sturdy business behind it. For the workflow it was built for, it is good. Epistles is a different shape of product for a different shape of inbox, one that does not assume your desk is the centre of your reading. If yours is the shape this page describes, our front door is here.