is
 expensive for a specific MimeMultipart subclass, then it
 might itself want to track whether its internal state actually
 did change, and do the header updating only if necessary.</div>
<dl>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="../MessagingException.html" title="class in jakarta.mail">MessagingException</a></code> - for failures</dd>
</dl>
</li>
</ul>
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<h4>writeTo</h4>
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