Recently users have begun to experience fails when sending mail with many addressees on both the To: and Cc: lines. Sending the message causes a service error dialog and the mailbox.log shows the following:

2008-11-03 17:22:33,129 INFO [btpool0-8066] [name=<>;aname=<>.gov;mid=2;ip=10.2.65.45;ua=Zimbra WebClient - FF3.0 (Win)/5.0.4_GA_2101.RHEL4;] mailbox - Added message: id=10484, digest=HoDiTveevFRwbjS2wN8+w8C+zhg=, folderId=5, folderName=Sent
2008-11-03 17:22:35,220 WARN [btpool0-8066] [name=<>;aname=<>;mid=2;ip=10.2.65.45;ua=ZimbraWebC lient - FF3.0 (Win)/5.0.4_GA_2101.RHEL4;] smtp - exception occurred during SendMsg
com.zimbra.cs.mailbox.MailSender$SafeMessagingExce ption: Broken pipe; chained exception is:
java.net.SocketException: Broken pipe
at com.sun.mail.smtp.SMTPTransport.sendCommand(SMTPTr ansport.java:1551)
at com.sun.mail.smtp.SMTPTransport.sendCommand(SMTPTr ansport.java:1538)
at com.sun.mail.smtp.SMTPTransport.close(SMTPTranspor t.java:683)
at javax.mail.Transport.send0(Transport.java:171)
at javax.mail.Transport.send(Transport.java:98)
at com.zimbra.cs.mailbox.MailSender.sendMessage(MailS ender.java:445)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(M ailSender.java:249)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(M ailSender.java:115)
at com.zimbra.cs.service.mail.SendMsg.doSendMessage(S endMsg.java:184)
at com.zimbra.cs.service.mail.SendMsg.handle(SendMsg. java:150)
at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:391)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:250)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:156)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:266)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:727)
at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:177)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:820)
at org.mortbay.jetty.servlet.ServletHolder.handle(Ser vletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1093)
at org.mortbay.servlet.UserAgentFilter.doFilter(UserA gentFilter.java:81)
at org.mortbay.servlet.GzipFilter.doFilter(GzipFilter .java:132)
at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1084)
at org.mortbay.jetty.servlet.ServletHandler.handle(Se rvletHandler.java:360)
at org.mortbay.jetty.security.SecurityHandler.handle( SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(Se ssionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(Co ntextHandler.java:716)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebA ppContext.java:406)
at org.mortbay.jetty.handler.ContextHandlerCollection .handle(ContextHandlerCollection.java:211)
at org.mortbay.jetty.handler.HandlerCollection.handle (HandlerCollection.java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:139)
at org.mortbay.jetty.handler.RewriteHandler.handle(Re writeHandler.java:176)
at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:139)
at org.mortbay.jetty.Server.handle(Server.java:313)
at org.mortbay.jetty.HttpConnection.handleRequest(Htt pConnection.java:506)
at org.mortbay.jetty.HttpConnection$RequestHandler.co ntent(HttpConnection.java:844)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser. java:644)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpPa rser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnec tion.java:381)
at org.mortbay.io.nio.SelectChannelEndPoint.run(Selec tChannelEndPoint.java:396)
at org.mortbay.thread.BoundedThreadPool$PoolThread.ru n(BoundedThreadPool.java:442)
2008-11-03 17:22:35,220 INFO [btpool0-8066] [name=<>;aname=<>;mid=2;ip=10.2.65.45;ua=ZimbraWebC lient - FF3.0 (Win)/5.0.4_GA_2101.RHEL4;] SoapEngine - handler exception
com.zimbra.common.service.ServiceException: system failure: MessagingException
ExceptionId:btpool0-8066:1225732955220:a94f382e41cb2925
Code:service.FAILURE
at com.zimbra.common.service.ServiceException.FAILURE (ServiceException.java:253)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(M ailSender.java:325)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(M ailSender.java:115)
at com.zimbra.cs.service.mail.SendMsg.doSendMessage(S endMsg.java:184)
at com.zimbra.cs.service.mail.SendMsg.handle(SendMsg. java:150)
at com.zimbra.soap.SoapEngine.dispatchRequest(SoapEng ine.java:391)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:250)
at com.zimbra.soap.SoapEngine.dispatch(SoapEngine.jav a:156)
at com.zimbra.soap.SoapServlet.doPost(SoapServlet.jav a:266)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:727)
at com.zimbra.cs.servlet.ZimbraServlet.service(Zimbra Servlet.java:177)
at javax.servlet.http.HttpServlet.service(HttpServlet .java:820)
at org.mortbay.jetty.servlet.ServletHolder.handle(Ser vletHolder.java:487)
at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1093)
at org.mortbay.servlet.UserAgentFilter.doFilter(UserA gentFilter.java:81)
at org.mortbay.servlet.GzipFilter.doFilter(GzipFilter .java:132)
at org.mortbay.jetty.servlet.ServletHandler$CachedCha in.doFilter(ServletHandler.java:1084)
at org.mortbay.jetty.servlet.ServletHandler.handle(Se rvletHandler.java:360)
at org.mortbay.jetty.security.SecurityHandler.handle( SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(Se ssionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(Co ntextHandler.java:716)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebA ppContext.java:406)
at org.mortbay.jetty.handler.ContextHandlerCollection .handle(ContextHandlerCollection.java:211)
at org.mortbay.jetty.handler.HandlerCollection.handle (HandlerCollection.java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:139)
at org.mortbay.jetty.handler.RewriteHandler.handle(Re writeHandler.java:176)
at org.mortbay.jetty.handler.HandlerWrapper.handle(Ha ndlerWrapper.java:139)
at org.mortbay.jetty.Server.handle(Server.java:313)
at org.mortbay.jetty.HttpConnection.handleRequest(Htt pConnection.java:506)
at org.mortbay.jetty.HttpConnection$RequestHandler.co ntent(HttpConnection.java:844)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser. java:644)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpPa rser.java:211)
at org.mortbay.jetty.HttpConnection.handle(HttpConnec tion.java:381)
at org.mortbay.io.nio.SelectChannelEndPoint.run(Selec tChannelEndPoint.java:396)
at org.mortbay.thread.BoundedThreadPool$PoolThread.ru n(BoundedThreadPool.java:442)
Caused by: com.zimbra.cs.mailbox.MailSender$SafeMessagingExce ption: Broken pipe; chained exception is:
java.net.SocketException: Broken pipe
at com.sun.mail.smtp.SMTPTransport.sendCommand(SMTPTr ansport.java:1551)
at com.sun.mail.smtp.SMTPTransport.sendCommand(SMTPTr ansport.java:1538)
at com.sun.mail.smtp.SMTPTransport.close(SMTPTranspor t.java:683)
at javax.mail.Transport.send0(Transport.java:171)
at javax.mail.Transport.send(Transport.java:98)
at com.zimbra.cs.mailbox.MailSender.sendMessage(MailS ender.java:445)
at com.zimbra.cs.mailbox.MailSender.sendMimeMessage(M ailSender.java:249)
... 33 more


The postfix config param for number of addressees is set to 1000. The zimbra log on the mta seems to show a connection being made and broken when these fails occur. Any suggestions?