Hugo was perhaps a little cryptic. As I understand it there is no facility to edit a members post.
Even as an administrator, the best you can do is reply to a message, quote the original text and edit the contents of the quote. Obviously, your post should make clear the way in which the quote has been edited and the reasons for it (e.g. to remove abusive language or off-topic content).
Then you can delete the original post (Preferably, move it to a hidden sub-forum, so you can reinstate the original post, if you change your mind about you edit).
Have you solved your problems with the mail list permissions? If not please give more detailed symptoms.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.