essage body, possibly multipart (arbitrarily deep). 
</p>

<p class=parameters>
The only parameter of the function is a table describing the message.
<tt>Mesgt</tt> has the following form (notice the recursive structure):
</p>

<blockquote>
<table summary="Mesgt table structure">
<tr><td><tt>
mesgt = {<br>
&nbsp;&nbsp;headers = <i>header-table</i>,<br>
&nbsp;&nbsp;body = <i>LTN12 source</i> or <i>string</i> or 
<i>multipart-mesgt</i><br>
}<br>
&nbsp;<br>
multipart-mesgt = {<br>
&nbsp;&nbsp;[preamble = <i>st