With permission from this esteemed body, the issue was discussed and Muon posted the following on the Forum Community Guidelines as the general policy to follow:
There have been some questions about the use of personal messages (pm's) in posts. The Terms of Service are not completely clear, so after some moderator discussion we have come up with this policy based on what is in the Terms of Service.
The Terms of Service forbid posts which are invasive of a person's privacy. This is interpreted to include posting the contents of a pm without the consent of the sender. Moderators may share pm's specifically related to moderating duties in the Moderators Corner (aka the Cave). Users playing games on the Forum may give blanket consent to have pm's specifically related to the game posted on the Forum in threads related to the game. Even with the consent of the sender pm's may not be posted on the Forum if they would violate the Terms of Service by containing material which is "false, defamatory, inaccurate, abusive, vulgar, hateful, harassing, obscene, profane, sexually oriented, threatening, invasive of a person's privacy, adult material, or otherwise in violation of any International or United States Federal law".
