In rare occasions, Apple Mail will show the message "This message has no content". Despite what Apple Mail shows, the e-mail may contain a message but Apple Mail is unable to show this.

A solution could be to use the webmail client to view your e-mails or switch to a different application, such as Airmail (which hooks into Apple Mail).

We do not know what causes the error. It is possible that the e-mail contains a technical formatting error which may put Apple Mail off guard. If this is the case, the formatting is done wrong by the sender and not by the server. The sender can try to use a different application in order to resolve the problem.