Settings -> Domains -> Team Settings -> Masked email domain.
Disclosure - I work at 1Password, though I had only tangential involvement in this effort
Disclosure - I work at 1Password, though I had only tangential involvement in this effort
Settings -> Domains -> Team Settings -> Masked email domain
It will default to fastmail.com, but easy to change it.
The full "it just works" integration seems to only work between 1password and fastmail directly.