Instead of a fixed sender, it can now also be selected from a dropdown. This requires a 'Field Validation' entry for 'm_letter' / 'emaildd'. A 'Y' in the first position of the default value activates the dropdown, followed by a semicolon and the definition of the email address(es):
'U': from the user master data
'D': default sender
'L': from the corresponding letter
Several senders can be entered here, separated by a comma; the order is also the order of the email addresses in the dropdown.