Hi kittylester, if a user deletes their account or messages, then all messages in the chain are removed, including your own, we're afraid.
It’s something that we put in place in the run up to GDPR, because we took the view that in situations like this, we need to privilege the right of users to delete their data.
In the case of PMs, messages by poster A can often contain personally identifying information about poster B. Because we’re putting poster B’s right to delete her data above other concerns, when poster B deletes a PM that was sent to her, the PM is deleted from our servers and will disappear from poster A’s ‘sent’ folder .
Likewise, if poster B de-registers or asks us to delete all her data, we think she will rightly expect PMs between herself and poster A to be deleted from our servers. That means they’ll also disappear from poster A’s ‘sent’ folder. Hope that explains things a bit more fully. 