Address inefficiencies and possible misfunction over delegated mailboxes in other user namespace
Summary: Resolves T2582
Test Plan: None
Reviewers: PyKolab Developers, machniak, vanmeeuwen
Reviewed By: PyKolab Developers, vanmeeuwen
Subscribers: adomaitis, machniak, PyKolab Developers
Maniphest Tasks: T2582
Differential Revision: https://git.kolab.org/D485