phpBB core's code takes care of everything that's related.
Thanks for the info. I had changed the first one to unlimited (which makes me a bit nervous but we shall see). Never touched the second one, but when I checked it just now it was set to 0 (unlimited) already so I don't know what was going on there. For now, everything seems to be working so I guess we'll see. I may experiment with some test posts and test settings in order to prevent anything crazy from happening with huge attachments.