Fix broken links found by "make linkcheck". scipy.org seems to be done right now, so I could not verify links going there.
diff --git a/Doc/library/mailbox.rst b/Doc/library/mailbox.rst
index 51cda8a..92f37cb 100644
--- a/Doc/library/mailbox.rst
+++ b/Doc/library/mailbox.rst
@@ -602,7 +602,7 @@
`nmh - Message Handling System <http://www.nongnu.org/nmh/>`_
Home page of :program:`nmh`, an updated version of the original :program:`mh`.
- `MH & nmh: Email for Users & Programmers <http://www.ics.uci.edu/~mh/book/>`_
+ `MH & nmh: Email for Users & Programmers <http://rand-mh.sourceforge.net/book/>`_
A GPL-licensed book on :program:`mh` and :program:`nmh`, with some information
on the mailbox format.