em client suddenly stopped keeping sent messages

For no apparent reason, and with no known alterations to any settings, eM has suddenly taken to not keeping copies of Sent emails for my Hotmail/Outlook Account.

I have checked through all the Account settings but am unable to find anything “dodgy”.
When I send anything from my GMX Account, a copy is retained in the Sent folder, as one would expect.

All Sent messages are in my Hotmail/Outlook Account, just not replicated in eM Client, despite having been sent from there.

Has anyone else had such an experience please – or got any ideas as to how it can be fixed??

Thank you,