I don't have Unlimited. I pay for Mail Plus. I also pay for SimpleLogin and Bitwarden. By moving to Unlimited I get SimpleLogin included and could ditch Bitwarden.
I don't see a way to import from SimpleLogin with Fastmail so don't see it being an option anyway. I really don't want to manually create 350 aliases.
When I get on my PC I will look again at my options. Thanks for your input.