Fastmail on iPhone: in one inbox with your other mail

By Manish, who makes LocalInbox · Facts checked November 2026

In short

Fastmail makes its own free iPhone app for Fastmail accounts. LocalInbox is for Fastmail users who have other accounts too: it puts Fastmail in one inbox beside Gmail, iCloud and any IMAP account on iPhone and iPad, on the App Store, and has Apple Intelligence write summaries and suggested replies on the device. It connects with an app password.

Fastmail on an iPhone today

Fastmail – Email & Calendar is free on the App Store, for iOS 15.4 or later, and manages Fastmail's mail, calendars and contacts. Its in-app purchase is a Fastmail plan.

How LocalInbox works with Fastmail on iPhone

It connects over IMAP with an app password made in Fastmail's settings.
Fastmail sits in the unified inbox with your other accounts, sorted the same way.
Search on Server asks Fastmail for older mail that isn't on your iPhone yet.
Summaries, suggested replies, Draft with AI, Rewrite and Ask your mailbox are written by Apple Intelligence on the iPhone or iPad itself (iOS 26 on a supported device). There's no AI cloud, and no LocalInbox server.
The password is kept in the iOS Keychain and sent only to the mail server.

The iPhone inbox in Harbor: every account together, with All, Primary, Updates and Promos tabs and Needs reply labels — Screenshots from the iPhone Simulator, on made-up demo mail. On an iPhone, Apple Intelligence writes the summaries and answers, so its words will differ.

A conversation on iPhone with an on-device summary and an Add to Reminders action — Screenshots from the iPhone Simulator, on made-up demo mail. On an iPhone, Apple Intelligence writes the summaries and answers, so its words will differ.

Set up Fastmail on iPhone

Make an app password for LocalInbox on Fastmail integrations. One you made for your Mac works too.
Open LocalInbox on your iPhone or iPad. With no account yet, it opens on Add Account; later, it's in Settings › Accounts.
Choose Fastmail and enter your address.
Paste the app password, and tap Add. LocalInbox fills in the server settings itself and starts syncing.
Already have the account in LocalInbox on your Mac? Choose From your Mac in Add Account instead, and scan the code in the Mac's Settings › Accounts › Set Up iPhone…. There's nothing to paste.

Server settings and what to do if it doesn't connect: Fastmail IMAP and SMTP settings, with an app password.

Sources

Facts about Fastmail's own apps were checked in November 2026 and can change. Facts about LocalInbox come from its own documentation.

App Store: Fastmail – Email & Calendar

Questions

Should I use LocalInbox or Fastmail's app?

Fastmail's app is made for Fastmail alone, with its calendar and contacts. LocalInbox is a mail app for several accounts at once, with AI on the device. Both can use the same account.

Do I have to sign in again if I use LocalInbox on my Mac?

No. On the Mac, open Settings › Accounts › Set Up iPhone…. On the iPhone or iPad, Add Account › From your Mac scans the code. Check that both show the same four digits and allow it on the Mac, and your accounts come over your Wi-Fi with their passwords, encrypted, never through the internet. Proton Mail stays on the Mac. https://localinbox.app/features/set-up-iphone-from-mac

How much does LocalInbox for iPhone cost?

The app is a free download with a 7-day trial with every feature, started with a tap. Then one purchase unlocks it for good: $29.99, in the app or on localinbox.app. No subscription.

Do I pay again for the iPhone if I have LocalInbox on my Mac?

No. Bought LocalInbox for Mac? Your licence key unlocks it here too. It's one licence for the Mac, iPhone and iPad, on up to 3 devices. Buying in the iPhone app instead costs the same and gets you a licence key for your Mac in Settings › Unlock LocalInbox.