I can only say again that DAVx⁵ does not delete collections from the server unless it’s explicitly requested by the user and confirmed in the UI. Also, we have never heard such a thing before, which is strange when you think how many people uninstall DAVx⁵. Will mark this is invalid until steps to reproduce or any other indications for this problem are given.

Thanks for looking into this. I didn’t provide any logs because I’m unable to anonymise them without potentially destroying useful information. I’ll try reproducing the issue with a new contact and post a log for that. Unfortunately I can’t say much about the server. I am using the address book provided by Posteo but I don’t know what they use internally. And as to why I’m still adding “ring:” to the IMPP string: It’s actually automatically added by the Ring app. I guess that’s simply the format of their IDs. EDIT I was pretty sure the issue was due to the new value of the IMPP field since sync failed for the exact two contacts that I had linked with their Ring IDs. It must have been something else though, since I have also been unable to reproduce the problem with a fresh contact. I have worked around the issue by deleting and re-creating both problematic contacts. I guess this thread can be closed now. Thanks for your time.

Hello, Thanks for your suggestion. What exactly do you think should be encrypted and where/when/how? If you want to protect the transport layer, you have to use TLS. Just using a symmetric cipher won’t bring any benefits because well-negotiated symmetric encryption is the essential part of a TLS connection. On the application layer, a CalDAV/CardDAV server has to know all data, because it needs to understand and process it. This is how CalDAV and CardDAV work. It’s not possible to send encrypted data to a CalDAV/CardDAV server and it wouldn’t make any sense, too. For instance, a server must be able to filter all events and return only the ones of the last 90 days. This can’t work if the server doesn’t understand the data (because it’s encrypted). So, if you want to protect your server, you will have to protect it physically and use disk encryption. If you want to protect your Android device from unauthorized usage, you can use full-disk encryption together with an appropriate locking mechanism.