Hi Jan.
5 Jears old, missing security fixes, …
Please update ASAP.
Some time ago, we expanded the function and removed the receiver infrastructure.
The message is therefore correct.
We will hardly be able to clarify what is going wrong with your database here in the community forum.
Especially not on such an old version.
As a commercial user, you can and should make use of our business support:
https://www.egroupware.org/en/professional-support
We will also support you with the update if necessary.
Stefan