Allowing deletion of private chat threads is on the backlog.Thierry Alen commented
what about EU Law GDPR? right to be forgotten including all data! So product is not GDPR compliant for as far we can see. please advice if we are wrong. Right to be forgotten means deleting all details including conversation history. This is also the main raison Skype all versions is not suitable for proper business. An example of this is even mentioned on this third party website we do use at the moment .