Request to be able to disable Sieve integration

In the Cyrus (IMAP/POP3) service, there's an area for a Sieve server address, port, and transport encryption. All are required '*' when adding an IMAP server.

We use SoGo for vacation responses, and filtering, which sets its own Sieve filter rules, so we want the ability to disable the sieve sever, and not attempt modifications to the user's sieve filters when changing vacation messages and related things.

As with IP assignment modifications, this could be a professional services contract.