I was about to ask the same question as I'm still using the old MsgPlus. There, you needed a StuffPlugin to be able to have that feature. Now it appears that some functions are integrated already in the new MPL but since I haven't installed it yet, I don't know if that's the case with the mentioned feature too. It really is an important feature to me as well, being able to se when a contact closes / opens a conversation. Can someone confirm this is avaiable in a new version (integrated or as a script add-on). It's that important to me that I don't think I'll switch to the new version until it's confirmed it supports it
