Using New Outlook on Windows for professional communication and productivity
Thanks for the nice tip D A K, unfortunately it doesn't work in current versions, even on the desktop (Outlook for M365 MSO version 2405). If you disable message previews, you'll get something which seems to work (a cursor in the field), but you won't actually be able to type or even paste text inside.
This has been reported since 2012 for individual emails:
- Adding Comments To E-mail in Custom Column (Outlook 2010)
- Outlook 2013: Custom columns in emails not editable in Conversation View (Outlook 2013)
Unfortunately, although Microsoft recommended this solution as recently as 2022, that thread is now broken and locked, and Microsoft has since acknowledged in How do I add a note to an email using outlook? - previous thread unresolved that this feature is just missing.