I have for some years used one mailbox and one outgoing mail server (from phone coop) together with thunderbird identities to specify different email 'from' addresses

This email provider is withdrawing the service so i have to find a new one. I have tried Fasthosts email, but that rejects Thunderbird identities (because of spoofing checks?). How can I determine which new email provider can cope with Thunderbird identities ? Clive