after backup restore - just log in as restored user, and check this menu item.
This notification just tells You that CatchAllEmail configured by default now, so when letter will come to non existent mailbox - sender will be notified that this mailbox doesn't exist. that's all. You can configure another actions - if you need.
Price apologies for the simple doubts, because I'm new to DA.
Thanks @Zhenyapanfor the contribution!
DA technical support sent me this answer below and I think it could be useful if another newbie has this same question.
Code:
Hello,
This error can be safely ignored.
It's a catchall setting that is strongly not recommended to use.
Catch all with :fail: is the default and recommended setting as it was set on your server.