I'm able to send pms to anyone whose messaged me prior to my ban. So I can reply to any conversation I've had back from 2010. I'm not sure if that's allowed? Also I haven't messaged anyone just one user to test it out because I had no idea I wasn't allowed to until I tried messaging someone else and it wouldn't let me.
See if it works. The messages still appear as does the reply option etc. But when you try to send it, it doesn't allow you to do so. Or at least it doesn't for me.