The subject of the e-mail cannot be changed.

[darkphex]

Dear O365 Team,

I have the problem that I can change and output the message subject in my code, but unfortunately this change is not executed and saved in Outlook.

Is this not possible, or can it be bypassed somehow?

else: print ("Checking...") message.mark_as_read() message.subject = subject + " // TEST" message.save_message() print(message.subject)

[alejcas]

For now, the subject can only be modified when the message is a draft.

[joelwiesmann]

Or make use of my workaround in https://github.com/O365/python-o365/issues/576 ;-)