How to Sync Fastmail Calendar and Contacts (CalDAV/CardDAV)

Fastmail doesn't lock your calendar and contacts inside its own apps. Both are exposed over two open standards — CalDAV for calendars, CardDAV for contacts — which is the same protocol family that iCloud, Nextcloud, and most non-Google providers use. That's what lets a Fastmail calendar show up natively in the iPhone Calendar app, or a Fastmail contact sync into Android's people list, without installing anything from Fastmail at all.

The setup is the same shape everywhere: point your device at a Fastmail server URL, sign in with your Fastmail address, and authenticate with an app-specific password instead of your normal login. Where it differs is per platform, and that's usually where sync breaks — an app password typed as the account password, a URL missing the trailing account path, or an Android phone with no CalDAV support built in at all.

What CalDAV and CardDAV actually are#

CalDAV and CardDAV are open, vendor-neutral protocols for syncing calendars and address books over HTTPS — the same category of standard as IMAP for mail. A CalDAV server stores events as .ics files and hands them to any client that authenticates correctly; a CardDAV server does the same for contact cards. Because the protocol is public, Fastmail doesn't need a native app on every platform — it only needs to run a compliant server, which it does, and let the operating system's own calendar and contacts apps talk to it directly.

That's the whole reason this works on an iPhone with zero extra apps installed: Apple's Calendar and Contacts apps already speak CalDAV and CardDAV natively. Android is the outlier, and the platform differences table below explains why.

Before you start: what you need#

Three things have to be true before any client will hold a connection to Fastmail's calendar or contacts servers.

• A Fastmail plan that includes CalDAV/CardDAV. Fastmail's own account documentation states plainly that Basic plans do not include IMAP, SMTP, CalDAV, or CardDAV access — only the standard and higher tiers do. If sync fails with an authentication error on every attempt, check the plan first.
• An app-specific password, not your account password. Every CalDAV/CardDAV connection requires one, generated from Settings → Password & Security → App Passwords in the Fastmail web app. Give it a name you'll recognize later ("iPhone Calendar", "DAVx5 Android") — you'll thank yourself when you're revoking one two years from now.
• Your full email address as the username, domain included — not just the part before the @. Fastmail treats the whole address as the login for CalDAV/CardDAV, the same as it does for IMAP.
• A few minutes of patience on the first sync. A calendar with several years of events or a contact book in the thousands can take noticeably longer to pull down than the handful of seconds an email client needs to open an inbox — that's normal, not a sign the connection failed.

The server URLs#

This is the part that trips people up most, because the two protocols use different hostnames and, for contacts, a URL with a specific path baked in.

Steps: adding the account#

1. 1

   Generate an app password

   In the Fastmail web app, go to Settings → Password & Security → App Passwords → New App Password. Name it after the device or app you're connecting, then copy the generated password somewhere safe — it's shown once.

2. 2

   Open your device's account settings

   On iPhone/iPad: Settings → Calendar → Accounts → Add Account → Other → Add CalDAV Account (repeat under Settings → Contacts → Accounts for CardDAV). On macOS: System Settings → Internet Accounts → Add Account → Other → CalDAV or CardDAV Account.

3. 3

   Enter the server, username, and app password

   Server: caldav.fastmail.com or carddav.fastmail.com (no https:// needed on iOS/macOS — the field expects the hostname). Username: your full Fastmail address. Password: the app password from step 1, not your login password.

4. 4

   Let the device verify and create the account

   iOS and macOS will attempt to connect immediately. A success screen means the account is created; an error almost always means either the app password was typo'd, or the username is missing the domain.

5. 5

   Confirm what syncs

   On iOS, toggle Calendars and/or Reminders on for the new account. On macOS, check both Calendars and Contacts under the account's service list. Give the first sync a minute — a large contact book or years of calendar history can take longer than a typical IMAP folder.

Platform differences#

The protocol is identical everywhere; what changes is whether the operating system has a CalDAV/CardDAV client built in at all.

Why won't my Fastmail calendar sync?#

Almost every sync failure traces back to one of four causes, and they're worth checking in this order because the first two account for most support tickets.

• Wrong password type. The single most common cause — the account password was entered where an app password belongs. Fastmail's CalDAV/CardDAV servers reject the regular login password outright.
• Username missing the domain. "jane" instead of "[email protected]" authenticates against nothing.
• Plan doesn't include CalDAV/CardDAV. Fastmail's Basic tier excludes it entirely — the connection will fail the same way regardless of how correctly everything else is configured.
• Stale app password. If you revoked and regenerated an app password (say, during a security cleanup) without updating every device using it, that device's sync will start failing silently until you re-enter the new one.

Does Fastmail work with Google Calendar?#

Not as a direct, two-way sync — Google Calendar doesn't speak CalDAV for reading external calendars the way Apple's apps do. The practical workaround is a one-way subscription: Fastmail can publish a calendar's read-only iCalendar (.ics) feed URL, which Google Calendar can subscribe to under Settings → Add calendar → From URL. That gets Fastmail events visible inside Google Calendar, but edits made in Google won't write back to Fastmail. For genuine two-way sync, keep both calendars on CalDAV clients — Apple Calendar, Thunderbird, or a CalDAV-aware Android app — rather than routing through Google.

Sharing a Fastmail calendar with family#

Fastmail's own sharing (Settings → Calendars → the calendar's share icon) grants other Fastmail users read or read-write access inside Fastmail's own apps, which is the simplest option if everyone in the family already has a Fastmail account.

For a shared calendar to show up on a family member's phone via CalDAV instead, they add it as a separate CalDAV account of their own, using their credentials and the specific shared-calendar path Fastmail's sharing screen provides — this is different from adding your personal calendar again under their name, and Fastmail's contacts documentation shows the equivalent pattern for shared address books: a `.Shared` suffix appended to the owning account's address in the URL.

A faster way to keep everyone's calendar in sync#

None of the steps above are optional if you want a genuinely open, CalDAV-based setup — that's the trade-off for not being locked into one vendor's app. But once the accounts are wired up, the day-to-day friction usually isn't the protocol, it's remembering to check for scheduling conflicts, follow up on meeting replies, or file the calendar invite that arrived buried in an email thread.

AI Emaily reads Fastmail calendar invites and scheduling threads inline with your inbox, and can draft replies, flag conflicts, or turn a back-and-forth into a confirmed event without you leaving the thread — under Copilot mode, every draft still needs your approval before anything sends. It doesn't replace the CalDAV setup above; your calendar still lives on Fastmail's own servers and syncs the same way to every device. We build AI Emaily, and connecting a Fastmail account takes the same OAuth-style flow as the mail setup, with a 7-day free trial to see whether the calendar-aware drafting is worth keeping.