Melnikov Maks

1 - All user B actions are inside Thunderbird. When user B changes calendar of event to his own, he becomes the organiser instead of user A. Then user B...

Yes, I compared this, and ORGANIZER has been changed to user B. Correction: after that ORGANIZER changes and event could be deleted from B and C calendars. Calendar A contains...

Again. User B has READONLY access to calendar C. After user B action 1 (incorrect saving): - event in calendar B has changed organizer from A to B - event...

Correction: After user B action 2 (deletion): - event in calendar B has disappeared - event in calendar C has been cancelled (not disappeared) (maybe it's OK after action 1)

I'd offer the following: 1 - use access groups, especially synced LDAP groups, not groups from contacts. You can parse LDAP groups with standard LDAP tools. 2 - if some...