Masked Email Manager
Guide
Masked Email from 1Password and Bitwarden
Fastmail doesn't ship its own browser extension for Masked Email. Instead, two password managers plug into it directly, so an address can be generated and filled without a trip to Fastmail's settings first.
1Password
Connect the two accounts once: in 1Password.com, open the sidebar and go to Integrations, then Fastmail, and sign in to authorize it. From the Fastmail side, the same connection is under Settings → Privacy & Security → Masked Email → Connect to 1Password.
After that, click an email field on any signup page, choose Create Masked Email from 1Password's menu, then Fill Email. If more than one Fastmail account is connected, 1Password asks which one to use, and Regenerate gets a different address before you fill it, if the first one doesn't fit.
Blocking one later doesn't require opening Fastmail: open the 1Password extension, search for the address, and use the dropdown next to it for Block Incoming Emails or Unblock Incoming Emails. Deleting an address outright still needs Fastmail's own settings.
Bitwarden
Bitwarden's integration works differently: instead of connecting accounts, its username generator asks for a Fastmail API token scoped to Masked Email, the same kind Masked Email Manager itself uses. The API token guide covers creating one if you don't already have it for the app.
Paste that token into the API Access Token field in Bitwarden's generator settings, then generate a Masked Email from there whenever a signup form needs one. There's no live account link the way 1Password has one, so a revoked or expired token just stops the generator from making new addresses; it doesn't touch ones already created.
Either way, it's still a Fastmail Masked Email
Both integrations create addresses through Fastmail's own Masked Email feature, not a separate one of their own. An address made from a signup form in 1Password or Bitwarden shows up in Fastmail's settings and in Masked Email Manager exactly like one made from either of those directly, and can be blocked from whichever place is open at the time.
Prefer creating addresses without switching apps mid-signup? The create guide covers doing it from Fastmail's settings or from Masked Email Manager on your phone instead.