Thai characters getting mutated to garbage while mailing out

[sourjya]

Hello,
I'm facing this strange problem when trying to mail out emails written in Thai.

The recipient is receiving something that looks like the following:

?=
 =?UTF-8?B?4Liw4LiB4Liw4LiB4LijIOC4n+C5ieC4s+C4sOC4gQ==?=
Message-ID: <e8d86842349690225b70ea9f3589406f@mydomain.com>
X-Priority: 3
X-Mailer: PHPMailer (phpmailer.codeworxtech.com) [version 2.3]
MIME-Version: 1.0
Content-Type: multipart/alternative;
       boundary="b1_e8d86842349690225b70ea9f3589406f"


--b1_e8d86842349690225b70ea9f3589406f
Content-Type: text/plain; charset = "UTF-8"
Content-Transfer-Encoding: quoted-printable

=E0=B8=B0=E0=B8=81=E0=B8=A3 =E0=B8=9F=E0=B9=89=E0=B8=B3=E0=B8=B0=E0=B8=81=
=E0=B8=B0=E0=B8=81=E0=B8=A3 =E0=B8=9F=E0=B9=89=E0=B8=B3=E0=B8=B0=E0=B8=81=
=E0=B8=B0=E0=B8=81=E0=B8=A3 =E0=B8=9F=E0=B9=89=E0=B8=B3=E0=B8=B0=E0=B8=81=
=E0=B8=B0=E0=B8=81=E0=B8=A3 =E0=B8=9F=E0=B9=89=E0=B8=B3=E0=B8=B0=E0=B8=81=
=E0=B8=B0=E0=B8=81=E0=B8=A3 =E0=B8=9F=E0=B9=89=E0=B8=B3=E0=B8=B0=E0=B8=81

This is happening ONLY for Thai. I tried with a couple of other languages like Chinese and Bengali and those mails turned up just fine.

I found another thread on similar lines but no solutions anywhere.

Can anyone help me out here?

Thanks,
Sourjya

UPDATE
This behavior is exhibited ONLY when the SUBJECT of the Email contains Thai Characters.

If I send a mail with only English Characters is the subject (body contains only Thai text) - the mail goes through just fine and recipient is able to read. But even a SINGLE character of Thai in the subject line is screwing it up for good.

Any ideas?