in an incoming email I can click on the “From” address to add the contact to the address book. However there is no way to easily _add_ the email address to an _existing_ contact.
This is relevant as I have many contacts that only have a phone number, but no mail address saved yet (because they come synced from Smartphone).
Please add a button “add mail address to existing contact”.
Or you could do even better:
when user clicks on “From” field, check if there is already a contact with the respective name in the address book and then offer _either_ the creation of new contact _or_ enriching of old contact respectively.