8bit encoding is not reliable in e-mail. Many mail transport agents will remove the top bit of every byte in the mail body.
"\xD8\xA8\xD8\xB1\xD9\x8A\xD8\xAF" in UTF-8 bytes; remove the top bit from those bytes and you get ASCII
The way to get non-ASCII characters into a mail body is to set
Content-Transfer-Encoding to either
quoted-printable, and the encode the body with
quoted-printable is better if the mail is largely ASCII as it retains readability in the encoded form and is more efficient for ASCII. If the whole mail is Arabic,
base64 would probably be the better choice.)