Add a "See also" section with useful links. More should be added giving

pointers to information about the other mailbox formats; if anyone can
provide the information needed, please let me know!

Doc/lib/libmailbox.tex

@@ -84,6 +84,21 @@ messages start with the EOOH line and end with a line containing only
 \end{classdesc}
 
 
+\begin{seealso}
+  \seetitle[http://www.qmail.org/man/man5/mbox.html]{mbox -
+            file containing mail messages}{Description of the
+            traditional ``mbox'' mailbox format.}
+  \seetitle[http://www.qmail.org/man/man5/maildir.html]{maildir -
+            directory for incoming mail messages}{Description of the
+            ``maildir'' mailbox format.}
+  \seetitle[http://home.netscape.com/eng/mozilla/2.0/relnotes/demo/content-length.html]{Configuring
+            Netscape Mail on \UNIX: Why the Content-Length Format is
+            Bad}{A description of problems with relying on the
+            Content-Length header for messages stored in mailbox
+            files.}
+\end{seealso}
+
+
 \subsection{Mailbox Objects \label{mailbox-objects}}
 
 All implementations of Mailbox objects are iterator objects, and so