IMAP connection errors

[toolcaserp]

We are seeing connection errors with regard to the IMAP service. We are not seeing them for Pop3 connections...

2007-12-18 16:51:42,267 INFO [ImapSSLServer-9401] [] imap - [166.133.233.80] connected
2007-12-18 16:51:43,727 INFO [ImapSSLServer-9401] [name=john@domain.com;ip=166.133.233.80;] imap - user john@domain.com authenticated, mechanism=login
2007-12-18 16:51:59,196 INFO [ImapSSLServer-9401] [] ProtocolHandler - Exception occurred while handling connection
java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream. java:168)
at com.sun.net.ssl.internal.ssl.InputRecord.readFully (InputRecord.java:293)
at com.sun.net.ssl.internal.ssl.InputRecord.read(Inpu tRecord.java:331)
at com.sun.net.ssl.internal.ssl.SSLSocketImpl.readRec ord(SSLSocketImpl.java:789)
at com.sun.net.ssl.internal.ssl.SSLSocketImpl.readDat aRecord(SSLSocketImpl.java:746)
at com.sun.net.ssl.internal.ssl.AppInputStream.read(A ppInputStream.java:75)
at java.io.BufferedInputStream.fill(BufferedInputStre am.java:218)
at java.io.BufferedInputStream.read(BufferedInputStre am.java:237)
at com.zimbra.cs.tcpserver.TcpServerInputStream.readL ine(TcpServerInputStream.java:73)
at com.zimbra.cs.imap.TcpImapRequest.continuation(Tcp ImapRequest.java:54)
at com.zimbra.cs.imap.TcpImapHandler.processCommand(T cpImapHandler.java:108)
at com.zimbra.cs.tcpserver.ProtocolHandler.processCon nection(ProtocolHandler.java:212)
at com.zimbra.cs.tcpserver.ProtocolHandler.run(Protoc olHandler.java:179)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Wo rker.run(Unknown Source)
at java.lang.Thread.run(Thread.java:619)
2007-12-18 16:51:59,197 INFO [ImapSSLServer-9401] [] ProtocolHandler - Handler exiting normally

What can be done to diagnose the errors? They aren't consistent. They occur occasionally, not consistently.