I'll have to concede the losing sharing. There are still some frustrating things there, the DAV ACL model doesn't map very well to the Cyrus model which is base

I'll have to concede the losing sharing. There are still some frustrating things there, the DAV ACL model doesn't map very well to the Cyrus model which is based on IMAP permissions and there were a couple of bad bugs in there until recently. We're still running patches that I'd like to remove, but at least we finally understand the cause of lost acls and fixed it. I'd love to know more about deliverability issues - that's something we monitor closely, and we want to know if there are any silent blocks/drop rules anywhere that we can't monitor for!