After installing emclient 11, I get an error from Office Outlook stating no default email about 3-4 pop ups appear, and eventually I can get outlook to work, I use it for Calendar and to sync with icloud, It did the same in the Beta when I installed it.
First off make sure you are running the latest eM Client V11.0.1054 Official Release and not any previous Beta. You can download it if you don’t have that from the release history page. Before updating make a manual backup via “Menu / Backup” incase you need to restore for any reason. You can see when the backup os complete in Show Operations via the dropdown on the right of Refresh. Also close eM Client before updating.
If the offical release doesn’t fix it, then see the following threads for help.