It looks like UTF-8, but your example is not valid UTF-8. Perhaps the character set translation has corrupted it.If you think it might help, you can send me one of these e-mails. I cannot read Arabic, but I can tell you whether I see valid Arabic characters. My e-mail address is in my profile.
In the memo that you sent to me, the header specifies the charset ISO-8859-1. This is wrong. If I change it to Windows-1256, then I see Arabic immediately when I open the memo.So the text seems to be in Windows-1256. I think the mailer that sent it set the wrong header, and I think you can only fix this by using View - Encoding - Other… whenever it happens.