gnus-diary provides a function called
gnus-diary-check-message to help you handle the
X-Diary-* headers. This function ensures that the
current message contains all the required diary headers, and
prompts you for values or corrections if needed.
This function is hooked into the nndiary back
end, so that moving or copying an article to a diary group will
trigger it automatically. It is also bound to C-c C-f
d in message-mode and
article-edit-mode in order to ease the process of
converting a usual mail to a diary one.
This function takes a prefix argument which will force prompting of all diary headers, regardless of their presence or validity. That way, you can very easily reschedule an already valid diary message, for instance.