After two years of clingy messages, you should now be able to delete all your PMs in one fell swoop. Popular people rejoice!
As part of ongoing changes to DG there has also been a slight change made to the default settings for a new adventurer. New users will now start with the chat toggle set to new on top, by default. This will NOT affect your current setting and you don't need to do anything, just something for mentors to be aware of when talking with new people.