Typically I would handle citing an Ancestry message much like an email or instant message. However, Ancestry recently made some updates to their messaging system and there is no longer a way to create or view subject lines. I am thinking that in order to cite it correctly I would need to make one up. If that's the case, am I correct in thinking that the subject line should now be placed in brackets?
David Smith" to "Joe Jones", e-message communicated via Ancestry e-mail, 29 May 2019, [Jones Family Connection,] Ancestry, Privately held by Smith, London, England.