+.SS LOCKING AND \-unseen
+If you use the \*(lqUnseen-Sequence\*(rq profile entry, rcvstore could
+try to read and update its sequence state while another
+.B nmh
+process is also trying to do so. This can cause the sequence state to
+lose track. To avoid this just between asynchronous invocations of
+.BR rcvstore ,
+do not use it without an external locking mechanism, for example, a
+.IR procmailrc (5)
+local lockfile, if you use the \*(lqUnseen-Sequence\*(rq profile
+entry.