Please allow:

Custom send pgp key by key id (to override sender email if needed). This allows more flexible signing options. Permitted by fairmail

Custom recipient pgp key if it doesn't match any current key identity email (or if override option used)

a) customise by alias (eg. use x key for all emails to domain aaa.com - thunderbird allows this)

On the fly recipient key selection if recipient email not found in gpg keys. Fairmail allows this and its really useful.
This assists when using alias services such as addy.io where recipient email won't always match their pgp key id

thanks