multipart/mixed email. Comes with empty body. What's wrong?

sending an email:

From: <...>
X-Mailer: SnowBoss
Reply-To: <...>
X-Priority: 3 (Normal)
Message-ID: <[email protected]>
To: <...>
Subject: =?UTF-8?B?0JzQntCZIFNVQkpFQ1Q=?=
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="----------A4D921C2D10D7DB"

This is a multi-part message in MIME format.

----------A4D921C2D10D7DB
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit

MY TEXT
----------A4D921C2D10D7DB
Content-Type: text/html;
charset=utf-8
Content-Transfer-Encoding: 8bit

<html><b>BOLD</b></html>
----------A4D921C2D10D7DB
.

<250 Data received OK. //server response

and it comes with empty body. This only happens with multipart/mixed content (tried multipart/alternative - same story)

Solution

As Tomasz mentioned, the line where you are using the boundary, you must have two hyphen at the beginning of your boundary separarator. Check the following:

MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="frontier"

This is a message with multiple parts in MIME format.
--frontier
Content-Type: text/plain

This is the body of the message.
--frontier
Content-Type: application/octet-stream
Content-Transfer-Encoding: base64

PGh0bWw+CiAgPGhlYWQ+CiAgPC9oZWFkPgogIDxib2R5PgogICAgPHA+VGhpcyBpcyB0aGUg
Ym9keSBvZiB0aGUgbWVzc2FnZS48L3A+CiAgPC9ib2R5Pgo8L2h0bWw+Cg==
--frontier--

Also notice that at the last boundary, you have to put another two hyphens to indicate that it's the end.

Example taken from Wikipedia, see here.