Use your Microsoft 365 mailbox in a better client. Without leaving Microsoft.

Outlook on Microsoft 365 is a fine email service. The mailbox is fast, the spam filtering is competent, the calendar is the one your colleagues already use. This page is not about leaving it. It is about the client you read it through, especially if you also keep a personal Gmail, a Fastmail, or a ProtonMail next to your work inbox.

Microsoft 365 is the service. Epistles is a client.

A great deal of confusion in this category comes from the word “Outlook” meaning two different things. There is Outlook the mailbox, run by Microsoft on their Exchange Online infrastructure, where your mail actually lives. And there is Outlook the application, the software that talks to that mailbox, in any of its flavours: Outlook for Windows, the new Outlook for Mac, Outlook on the web, the Outlook mobile apps, and the various third-party clients that connect through Microsoft’s APIs.

Epistles is the second kind of thing. Your mail stays at Microsoft. Your calendar stays at Microsoft. Your contacts, your filters, your shared mailboxes, your retention policies, your administrator, all of that stays exactly where it is. Epistles is the window you read through. Connecting an Outlook account to Epistles changes the application; it does not migrate, copy, or move your mail anywhere. You can disconnect tomorrow and Outlook on the web is still there, untouched.

MS Graph, not EWS.

Microsoft maintains two APIs for talking to a Microsoft 365 mailbox. The older one, Exchange Web Services (EWS), shipped in 2007 and is what most third-party clients still use, including a few that you would expect to know better. The newer one, the Microsoft Graph mail API, is the one Microsoft itself recommends and the one their own first-party software has been migrating to for years.

On 30 September 2025 Microsoft announced that EWS will be retired for Exchange Online. From 1 October 2026, the service will begin disabling EWS for tenants by default, and on 1 April 2027 it shuts off completely with no exceptions. The retirement applies only to the cloud; on-premises Exchange Server still supports EWS, but for Microsoft 365 and Exchange Online the clock is ticking. Any third-party client that still relies on EWS for Microsoft 365 has a forced rewrite ahead of it, and if they don’t finish the rewrite in time their users wake up one morning to a mailbox that no longer connects.

Epistles uses MS Graph from day one. There is nothing to rewrite. When April 2027 arrives, the app keeps working. This is not a marketing claim, it is the only honest reason to start a new Microsoft client in 2026: the API is the API, and Microsoft has been clear about which one is the future.

Real-time push, properly.

Microsoft 365 supports real-time push notifications through a SignalR channel called the OWA notification channel, the same one their own Outlook web client uses. We connect to it directly, so a new message appears in Epistles within a second of arriving at the server, with no polling and no wake-on-schedule pattern draining your battery.

The complication is that Microsoft has been migrating tenants from a legacy ASP.NET Framework SignalR transport to a newer ASP.NET Core SignalR transport, and a given Microsoft 365 organisation can be on either generation. Epistles detects which one the tenant runs from the negotiation response and adapts to both, including the protocol-level handshake and token-passing differences between them. Most third-party Outlook clients skip push entirely and poll every few minutes instead, which is why their mail feels a step behind. We thought it was worth doing properly.

One client, every account.

The reason we built Epistles, and the reason a Microsoft 365 user might prefer it over Outlook itself, is that almost nobody only has an Outlook account. The typical working life involves a work Microsoft 365 mailbox alongside a personal Gmail that has carried the family logistics for a decade, a Fastmail address that has outlasted three jobs, sometimes a ProtonMail for the political work, and a generic IMAP account that’s been on the same domain since 2003.

Outlook can connect to some of these. Microsoft has been quietly improving Outlook’s ability to add a Gmail account, and the new Outlook for Mac will take an iCloud address. The result is functional but not generous: every account that isn’t a Microsoft account in Outlook is treated as second-class. Categories disappear, labels become folders, the search runs against Microsoft’s server-side index of mail it had to copy from Google to make work at all, your Gmail filters live in one place and your Outlook rules in another. You can use it. It does not feel like home for the non-Microsoft half of your inbox.

Epistles takes a different approach. Each provider speaks its own native protocol. Microsoft 365 through MS Graph. Gmail through the Gmail API, with labels staying labels. Fastmail through JMAP, the protocol it was designed for. ProtonMail through Proton’s own API with OpenPGP decryption on your device. IMAP and SMTP for everything else. Each adapter is loaded only when you use it, so a Microsoft-and-Gmail user never downloads ProtonMail’s crypto code, and a mailbox that doesn’t use IMAP doesn’t pay for it.

The effect is one application, one settings panel, one keyboard map, with every account speaking the dialect it was meant to speak. Your Outlook calendar shows up alongside your Gmail labels and your ProtonMail’s encrypted threads, in a single window, on every device you read mail on.

How Epistles compares to other Outlook clients.

Outlook on the web (OWA)

Microsoft’s own browser client. Excellent for a single Microsoft 365 account, increasingly less so for two, no story at all for a non-Microsoft account next to it. Lives in a tab, not in your dock.

The new Outlook for Windows and Mac

Microsoft’s desktop replacement for the classic Outlook. Built on web technology, ties tightly to Microsoft 365, can add Gmail and iCloud through a server-side mirroring layer that makes them feel like guests. Memory footprint is widely complained about; not Microsoft’s priority to fix.

Classic Outlook for Windows

Decades of features, a deep integration with Office, and a reputation for being heavy. Microsoft has stated it is on a glide path to retirement; the new Outlook is the future they are pointing customers towards.

Apple Mail with Exchange

Native, fast, free, on macOS and iOS only. Connects to Microsoft 365 through Microsoft’s Exchange ActiveSync flavour, which is a separate protocol from both EWS and Graph and increasingly limited. Calendar invitations and categories work; advanced features and shared mailboxes do not.

Third-party clients still on EWS

A surprising number of long-standing email clients still talk to Microsoft 365 via EWS. They have a hard deadline of April 2027 to migrate to Graph or stop working. Worth asking your current client which API they use.

Epistles

MS Graph throughout. Real-time push via the OWA SignalR channel, both generations supported. macOS, Linux, iOS, and Android shipping today; Windows and a web app at app.epistles.com in build. Microsoft 365 next to Gmail, Fastmail, ProtonMail, and IMAP, each in its native protocol.

What you give up.

We are an email client, not an Outlook clone, and there are parts of the Microsoft ecosystem we don’t replicate. The honest list:

• Teams integration. Outlook’s deep ties to Teams chats, meetings, and presence are not in Epistles, and we have no plan to embed Teams. If you live in Teams, you will still want it open in its own application.
• Advanced calendar features. Epistles reads and writes Outlook calendar events through Graph, including invitations, recurring events, and scheduling. Shared calendars and delegated mailboxes work. Resource booking, scheduling assistant with free-busy across rooms, and Microsoft Bookings are things Outlook still does better.
• Microsoft 365 administrator features. Mail flow rules, compliance holds, eDiscovery, message tracing: those are administrator surfaces and stay in the Microsoft 365 admin centre where they belong. Epistles is a user’s client.
• Shared mailboxes and public folders are partially supported. Personal shared mailboxes work; the older Exchange public folders, which use a tree separate from regular mail, are limited.
• Copilot and Microsoft’s AI writing tools are not in Epistles and won’t be. We do not ship AI features that route your mail through a model provider; we don’t want that responsibility, and we don’t want your mail in those logs.

And on our own roadmap, snooze, send-later, and read receipts are not yet shipping. Outlook ships all three. We will, but they are not in the box today, which is honest.

Privacy.

Even using MS Graph, your Microsoft 365 mail travels directly between your device and Microsoft over Microsoft’s own API. Our servers are not in that path. We do not see message bodies, subjects, recipients, or attachments. The Cloud Vault holds your Microsoft OAuth refresh token as opaque ciphertext encrypted under a key derived from your Epistles password, which we don’t hold. The security page has the longer version.

If your inbox is the shape this page describes.

Microsoft 365 is the mailbox you have. Epistles is one of the better windows you can read it through, and it is the one that also lets your other accounts in, each in its own dialect, on every device you keep them on. Fifteen-day trial, no card up front, three accounts on Free afterwards. Request early access, or read the rest of the site.