Problem with encoding in email subject - 6.3 or 6.4

Hi Everyone,

I have a problem with subject encoding. My email subject contains these chinese characters - 意向客户-参展预订-CN官网渠道 (emailSubject is the property name in the JCR to store this value) but when a User receives an email, these characters are shown like this - 意向客户-参展预订-CNå®˜ç½‘æ¸ é“

I have checked in the Publisher Logs interacting with SMTP Server and I'm getting this in the logs:

Subject: =?UTF-8?B?w6bChMKPw6XCkMKRw6XCrsKiw6bCiMK3LcOlwo/CgsOlwrHClcOp?=

=?UTF-8?B?wqLChMOowq7Coi1DTsOlwq7CmMOnwr3CkcOmwrjCoMOpwoHCkw==?=

MIME-Version: 1.0

Content-Type: text/plain; charset=UTF-8

Content-Transfer-Encoding: quoted-printable

Template is defined as:

From: noreply@testmail.co.uk

Subject: ${emailSubject}

Author name: ${authorName}

${formData}

All other custom fields (like firstName, lastName etc) looks fine and enoding/decoding also looks Ok for these fields:

title: =E5=A4=AB=E4=BA=BA

salutation: =E5=8D=9A=E5=A3=AB=E6=95=99=E6=8E=88

firstname: =E9=9C=80=E8=A6=81=E5=A1=AB=E5=86=99=E7=A7=B0=E8=B0=93

surname: =E9=9C=80=E8=A6=81=E5=A1=AB=E5=86=99=E7=A7=B0=E8=B0=93

Seems to be encoding issue for the Subject Field.

Has anyone encountered this issue while using EmailService.sendEmail(var1, var2, var3)?