s value to be out of date.
 This value might only be updated when a folder is first opened.
 Note that messages may have been appended to the folder
 while it was open and thus this value may be out of
 date. <p>

 If the value is unknown, -1 is returned.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the UIDNEXT value, or -1 if unknown</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="MessagingException.html" title="class in jakarta.mail">MessagingException</a></c