I can reply via PM to a post by flagging it and selecting “Send
<username> a message”:
If I send a PM to someone that way, they withdraw their post, and 24 hours later it gets deleted, system autoresponds to the PM like it was a flag, saying the post has been deleted. For instance, a user was asking if they posted in the right category, I PMed them saying they did, and they withdrew their post. 24 hours later when it was deleted, system responded like it was a flag. This was on our Discourse forum – not the Meta.