                          of existing values</dd>
<dd><code>java.lang.IllegalStateException</code> - if this Part is 
                                obtained from a READ_ONLY folder</dd>
<dd><code><a href="MessagingException.html" title="class in jakarta.mail">MessagingException</a></code> - for other failures</dd>
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<h4>addHeader</h4>
<pre class="methodSignature">void&nbsp;ad