Index: openacs-4/packages/acs-mail/tcl/acs-mail-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-mail/tcl/acs-mail-procs.tcl,v
diff -u -r1.9 -r1.9.4.1
--- openacs-4/packages/acs-mail/tcl/acs-mail-procs.tcl	3 Oct 2003 12:31:28 -0000	1.9
+++ openacs-4/packages/acs-mail/tcl/acs-mail-procs.tcl	23 Nov 2005 03:49:22 -0000	1.9.4.1
@@ -399,7 +399,13 @@
 } {
     Process the outgoing message queue.
 } {
-    db_foreach acs_message_send {
+    # Make sure that only one thread is processing the queue at a time.
+    if {[nsv_incr acs_mail process_queue_p] > 1} {
+        nsv_incr acs_mail process_queue_p -1
+        return
+    }
+        
+        db_foreach acs_message_send {
         select message_id, envelope_from, envelope_to
             from acs_mail_queue_outgoing
     } {