If the user has registered and logged in then you will already know who they are. But they may want to quote a different email address from the one they registered with.
So you could keep much the same look and feel for registered users by using the same three pieces of data but presenting them slightly differently:
- name (either on the form itself, or in a disabled text field)
- sender email address (filled in in a text field, ready to be changed if necessary)
- message body
You should also have a method of signalling "I'm someone else" which would log out the logged-in user and revert to the unregistered form.
A refinement would be to have a further option (probably hidden until needed) to signal that the registered email address should be changed to the email address actually used in the form.
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