Fastmail on the desktop: one window for mail and calendar

Fastmail desktop is one of the few searches in this category with a straightforward answer: the app exists. Fastmail publishes desktop builds for macOS on both Apple Silicon and Intel, alongside Windows and Linux, and the download page lists them plainly. Anyone who arrived here expecting to be told that no such thing exists can stop reading, download it, and be finished in five minutes.

The question worth spending time on is the one that comes after. A single official app covers a single mailbox well. It does not cover two mailboxes signed in at once, it does not bring browser extensions with it, and it does not put mail next to the other three web tools a working day runs on. Those are the cases where building a window from the web interface is the better answer, and the choice between the two is easier once it is clear exactly what each one gives up.

What Fastmail ships for the desktop

The download page lists four desktop builds and two mobile ones.

Platform	Build listed
macOS	Apple Silicon, and a separate Intel build
Windows	x64
Linux	Flathub
Mobile	iOS and Android

The page describes the desktop app as a way to get fast, private email, calendars, and contacts, and describes the app overall as full featured with offline support, available for Windows, macOS, Linux, iOS, and Android. A beta channel is offered separately for anyone who wants earlier builds.

Two details are worth noting for a Mac. The app is distributed from Fastmail's own site rather than the Mac App Store, so updates come through the app rather than through Apple's updates list. And the service itself is paid, with a thirty day free trial offered from the same pages, which means an unused mailbox is not a costless thing to leave signed in.

Alongside the desktop builds, the iOS app is published on the App Store by Fastmail Pty Ltd, is free to download, and requires iOS 15.4 or later. A Mac App Store search returns third party mail clients from other developers rather than anything published by Fastmail, which is consistent with the desktop app being a direct download.

What the official app settles, and what it leaves open

For one mailbox, the official app is the correct choice and there is nothing clever to add. It has a Dock icon, a place in Command Tab, its own notification identity in System Settings, and offline support, which is the one thing no wrapped web page can supply.

Three situations fall outside it.

Two mailboxes at the same time. A work address and a personal address, or a personal address and one managed for a family member, are two signed in sessions. One application instance generally holds one, so the second lives in a browser anyway, and the arrangement ends up half in an app and half in a tab.

Browser extensions. Fastmail's own pricing page lists integrations with 1Password and Dropbox among the premium mail features, so the service is built with outside tools in mind. A password manager running as a browser extension, or a content blocker, does not load inside a native desktop app. Anyone whose habits depend on an extension in the mail window will notice its absence immediately.

Mail next to everything else. Mail is rarely the only web tool open. A calendar from another provider, a project tracker, a support inbox, and a bookkeeping page tend to travel with it. A single mail app does not help with those, and they go back to being tabs.

None of that is a criticism of the app. It is the normal shape of a native single purpose application, and it is exactly why the web interface route continues to matter.

Route one: Safari's Add to Dock

macOS Sonoma 14 added a way to turn any page into something that behaves like an app. Open the mailbox in Safari, choose File and then Add to Dock from the menu bar, name it, and click Add. Apple's documentation states what the result is.

A web app functions independently of Safari. It shares no browsing history, cookies, website data, or settings with Safari. In this way, it keeps your browsing separate, similar to using a Safari profile. What you do in a web app stays in the web app. Source: support.apple.com

That isolation is the whole trick for mail. Two Fastmail addresses become two web apps with two icons, each holding its own cookies, both signed in at the same time. Neither displaces the other, and no second browser is needed.

The app is saved into the Applications folder of the home folder and opens from the Dock or Spotlight. Its settings panel takes a custom name, a custom URL, and a custom icon, and there is a switch for whether the toolbar shows navigation controls at all. Apple also documents an unread count appearing as a red badge on the Dock icon, with one condition: the notification permission has to be granted inside the web app rather than in Safari. After that the app appears in System Settings under Notifications by its own name rather than a URL, which is how a mailbox gets its own alert style and its own Focus permission.

The limits are the macOS version, since Sonoma 14 or later is required, and the extensions, since only Safari extensions apply. Offline reading is also not part of this route, and that is the clearest argument for the official app.

Route two: Chrome's Install page as app

Chrome offers the equivalent on older versions of macOS. Its help pages describe opening the site, then choosing More, then Cast, save, and share, then Install page as app.

A web app is an app built for the web that you can access on any device. You can use web apps to have a website work as an app and access it on your computer or mobile devices through the launcher or home screen. Some web apps include extra features, like more storage to browse content offline, notifications, file system access, and icon badges. Source: support.google.com

The extra storage for offline browsing is relevant here, though it is a web platform capability rather than a promise about any particular mailbox. File system access matters too, since mail means attachments in both directions.

The catch is the profile. An app installed this way runs on the Chrome profile it was created from, so its session, cookies, and extensions belong to that profile. One mailbox is clean. Two mailboxes need two Chrome profiles created first, which moves the juggling rather than removing it.

Route three: a dedicated site to app tool

A tool that turns a website into a standalone Mac app is built for precisely the gaps listed above.

Profile isolation covers the two mailbox case properly. Each app is assigned its own browser profile, with cookies, sessions, history, and cache separated, so any number of addresses can be signed in permanently in parallel windows.

Extensions come from the Chrome Web Store and can be switched on or off per app. A password manager extension inside the mail window, and nothing else running there, is a sensible arrangement for a mailbox, and it is the thing a native app cannot offer.

Space Mode is the feature that suits mail best. Several sites combine into one application with a sidebar of icons for one click switching. A mailbox, a calendar from a different provider, and a shared team inbox become one window with three icons rather than three Dock entries. For anyone whose day already runs across several web tools, that is a bigger change than giving mail its own icon.

The engine underneath is selectable across Chrome, Chromium, Brave, Microsoft Edge, Vivaldi, Opera, and Chrome Canary, and the tool repairs its apps after a browser update rather than leaving them unable to launch, which was the standard failure of older wrapper utilities. Support reaches back to macOS 12, four major versions earlier than Safari's Add to Dock. The features page covers the rest, and the supported services list shows which sites arrive as presets out of more than three hundred, with anything else added by URL.

The four routes side by side

	Official desktop app	Safari Add to Dock	Chrome install as app	Site to app tool
macOS required	Apple Silicon or Intel build	Sonoma 14 or later	Whatever Chrome supports	macOS 12 or later
Offline mail	Yes, stated as a feature	No	Web platform storage only	Web platform storage only
Two mailboxes signed in at once	One instance, one session	Yes, two web apps	Needs two Chrome profiles	Yes
Browser extensions inside it	No	Safari extensions only	Chrome extensions from that profile	Chrome Web Store, per app
Mail beside other web tools	No	Separate apps	Separate apps	One app, sidebar switching
Cost	Included with a paid plan	Included with macOS	Free	Free for up to three apps

The decision reads straight off the table. Offline access or a single mailbox points at the official app, and it should be the default. Two mailboxes, a dependency on a browser extension, or a desire to keep mail beside the other daily tools points at a built window, and nothing stops both existing on the same Mac.

Four things to test before moving mail into a window

A mailbox does more work than most pages, and the extra work is where a stripped down window can disappoint. Fifteen minutes of testing settles it.

Send an attachment and receive one. That exercises the file picker in one direction and the download location in the other, and it confirms drag and drop from Finder into the window behaves as it does in a browser.

Click a link inside a message. A mail window with no tab bar has nowhere to put a new tab, so the sensible behaviour is handing the link to the default browser. Confirm which one happens before relying on it.

Grant the notification permission inside the window, then check System Settings under Notifications. The mailbox should appear there by its own name. Set the alert style and the Focus permission there rather than leaving them at whatever the browser had.

Quit the app and reopen it. That confirms the session survives a restart and reveals whether a two factor prompt reappears every launch. The guide covers the settings involved.

What to change first

Download the official app and use it for the main mailbox, because offline support is real and no wrapped page provides it. Then deal with the leftovers deliberately rather than by leaving them in tabs: a second address, a shared inbox, a calendar from another provider. Kagemusha is free for up to three apps, which is enough to give each of those a window and find out within a week whether the arrangement holds.