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Fastmail app password: create one for IMAP and SMTP
- Create it in Fastmail on the web, under Settings, and paste it into your mail app. Your normal Fastmail password never works in other apps.
- Accounts on the Basic plan can't create app passwords or use other mail apps.
- Fastmail lets you limit what each app password can reach and shows when and where it was last used.
Fastmail is strict about passwords, on purpose: the password you type on fastmail.com never works anywhere else. Thunderbird, Apple Mail set up by hand, a phone's mail app, a backup script or a service that sorts your inbox all need an app password made for them. The one exception: Thunderbird 115 or later can sign in through a Fastmail window instead.
The good news is that Fastmail's app passwords are more flexible than Google's, Apple's or Yahoo's. Here's how to create one, what each access option means and what goes wrong.
What an app password is
It's a separate code your provider creates for one app: the app opens your mail with it and never sees your real password. For the full picture of why it exists, when you need one and what the risks are, see what are app passwords.
Before you start
- A plan above Basic. Fastmail says users on the Basic plan "will not be able to use Fastmail on third-party mail clients or create app passwords" (Fastmail help).
- Fastmail on the web. App passwords are created in the web interface, not in the Fastmail app.
Create the app password
- Sign in to Fastmail on the web and open Settings → Privacy & Security.
- In Connected apps & API tokens, click Manage app passwords and access.
- Click New app password. If a Verify it's you box appears, type your password and click Continue.
- Pick a name from the list, or Custom… to type your own.
- Choose the access (see below).
- Click Generate password, copy it into your app, and check that the app connects before clicking Done.
On an iPhone, iPad or Mac, that last page also offers a QR code or a file that sets up the account for you.
The password is 16 random characters, without 0, 1, O or I, so it's hard to misread. Spaces and capital letters don't matter. Steps from Fastmail's help, checked on 26 October 2026.
Which access to choose
| Access | What it opens | Use it for |
|---|---|---|
| Mail, Contacts & Calendars (default) | Mail over IMAP, POP and SMTP; contacts (CardDAV); calendars (CalDAV) | A full mail app on a computer or phone |
| Mail (IMAP/POP/SMTP) | Your mail, nothing else | A mail app or a service that only reads or sorts mail |
| Contacts only, or Calendars only | Just that data | A calendar or contacts app |
| Files (WebDAV) | Your Fastmail file storage | Apps that sync files |
Give each app the least it needs. A service that sorts your mail has no reason to see your calendar.
Settings for your mail app
IMAP is how mail apps fetch your email, and SMTP is how they send it. From Fastmail's server names and ports:
| Server | Port | Security | |
|---|---|---|---|
| Incoming (IMAP) | imap.fastmail.com | 993 | SSL/TLS, not STARTTLS |
| Outgoing (SMTP) | smtp.fastmail.com | 465 (or 587 with STARTTLS) | SSL/TLS |
Username: the full username you signed up with, including the domain. Fastmail says other addresses "will not work", so not an alias or another address on the account.
When it doesn't work
"Password error" in the app
You typed your normal Fastmail password. Only the app password works.
Login fails with the right app password
- The username is an alias or a different address. Use the one you signed up with.
- The app password doesn't include mail access. Check it under Manage app passwords and access.
- The app password was disabled. Fastmail lets you disable and re-enable one without deleting it.
There's no option to create one
Your account is on the Basic plan. Fastmail doesn't allow third-party mail apps on it.
Check, disable or remove a code
Manage app passwords and access lists every code. Review access shows what it can reach, when it was first used and the last access, with date, IP address and rough location. You can Disable a code for a while or remove it for good; removing can't be undone. Fastmail never shows the password itself again.
Connecting Fastmail to MailTag
MailTag sorts each new Fastmail email into your own categories and signs in with an app password. Under Settings → Mailboxes → Connect mailbox, type your Fastmail address. MailTag recognizes Fastmail, also your own domain if Fastmail handles its mail. The Open Fastmail app passwords button opens the right page. Create a New app password, name it MailTag, choose Mail (IMAP/POP/SMTP) access, paste it and click Test & connect.
In Fastmail, your categories show up as colored marks on each email by default, with nothing moved; you can switch to folders later in Settings → Mailboxes. MailTag checks for new email every 5 minutes, never deletes anything and keeps the app password encrypted. In Fastmail's Review access you'll see exactly when MailTag last signed in. If you want an AI agent to work with your Fastmail mail, Fastmail has its own MCP server; see Fastmail MCP servers.
FAQ
Can I use my Fastmail password in Thunderbird or Apple Mail?
No. Every third-party app needs its own app password; the normal password gives a password error. The exception is Thunderbird 115 or later, which can open a Fastmail sign-in window instead.
Why can't I create an app password in Fastmail?
Accounts on the Basic plan can't use third-party mail apps or create app passwords. Moving to a higher plan unlocks it.
What username do I use with a Fastmail app password?
The full username you signed up with, including the domain. Aliases don't work.
Can I limit what a Fastmail app password can access?
Yes. When you create it you choose mail, contacts, calendars, all three, or files.
How do I see when an app password was last used?
Open Manage app passwords and access and choose Review access: it shows the last access with date, IP address and approximate location.
What are Fastmail's IMAP settings?
imap.fastmail.com, port 993, SSL/TLS (not STARTTLS), with your full username and the app password.