Help
Create a Fastmail app password with Contacts access. Use your full Fastmail login address, rather than an alias.
Choose groups from your personal address book, then download a separate setup profile for each iPhone, iPad, or Mac. Install it in Settings. Select this account as the default for new contacts.
After confirming the new account works, disable Contacts in the original Fastmail account on that device to stop syncing the full address book.
The service checks Fastmail every few minutes. Your device's Fetch schedule adds delay. On iPhone, pull down in Contacts → Lists to refresh now.
Removing someone from a selected group removes their device copy. Deleting a contact on a device deletes the actual Fastmail contact. Editing requires Fastmail write access.
This beta supports up to 2000 selected contacts, with a storage limit for large photos. Connecting a different app password resets device logins to protect your cached data; add your devices again afterwards.
OAuth sign-in will be available after Fastmail registers the integration. This service is independently operated.