There is a problem with the new wp_mail function.
If an email is sent to wp_mail() with a custom header of "Content-Type: multipart/mixed; boundary="frontier"", wp_mail() is a) not recognizing that a custom boundary has been set and b) using that custom boundary (in this case, "frontier") as the email character set (charset). This is producing malformed subject lines and messages in emails with non-western characters.
For example, PluginX sends an email to wp_mail(). The email's headers are formed correctly:
To: xxx@xxx.org
Subject: =?UTF-8?B?0KHRgNC/0YHQutC4INCa0YPQu9GC?=
Date: Mon, 15 Oct 2007 10:04:34 -0500
From: "xxx@xxx.org" <xxx@xxx.org>
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="frontier"
--frontier
Content-Type: text/plain; charset = "UTF-8"
Content-Transfer-Encoding: 8bit
Attached to this email is
xxx.sql.gz
Size:82 kilobytes
--frontier
Content-Type: application/octet-stream; name="xxx.sql.gz"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="xxx.sql.gz"
H4sIAAAAAAAAA5yMQQrCMBRE9znFQNdKWhQhWwu6sKgouLQ/yYeCNSn5UentzcITOLt585gKt5j8
--frontier
wp_mail() explodes and parses the email headers, incorrectly ascribing "frontier" as the Charset while assigning its own boundary:
To: xxx@xxx.org
Subject: =?frontier?B?0KHR?= =?frontier?B?gNC/?= =?frontier?B?0YHQ?= =?frontier?B?utC4?= =?frontier?B?INCa?= =?frontier?B?0YPQ?= =?frontier?B?u9GC?=
Date: Mon, 15 Oct 2007 10:04:34 -0500
From: "xxx@xxx.org" <xxx@xxx.org>
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="b1_49700ab183d95dd1680e0898d750b958"
--b1_49700ab183d95dd1680e0898d750b958
Content-Type: text/plain; charset = "frontier"
Content-Transfer-Encoding: 8bit
Attached to this email is
xxx.sql.gz
Size:82 kilobytes
--b1_49700ab183d95dd1680e0898d750b958
Content-Type: application/octet-stream; name="xxx.sql.gz"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="xxx.sql.gz"
H4sIAAAAAAAAA5yMQQrCMBRE9znFQNdKWhQhWwu6sKgouLQ/yYeCNSn5UentzcITOLt585gKt5j8
--b1_49700ab183d95dd1680e0898d750b958
PluginX's once correctly-formed email is now severely broken, using PluginX's custom boundary as a charset.
