Yes I think the ASSUMPTION whne receiving an e-mail is that we cannot post it anywhere.
Therefore by stating that one can post it,... is like saying I give you the freedom to post my e-mail, which removes the underlying privacy that is associated with all e-mails received.
So by default one should never post someone elses e-mail unles the poson says,.. OK to to post.
But I guess you knew all this,...?