http server - log:
[29/May/2006:17:44:37 +051800] usg197 httpd[6751]: General Critical: Not enough file 
descriptors to support 6000 sessions per process; Recommend ulimit -n 12851 or 87 
sessions per process.

pop server - log:
[29/May/2006:17:44:37 +051800] usg197 popd[6749]: General Critical: Not enough file 
descriptors to support 600 sessions per process; Recommend ulimit -n 2651 or 58 
sessions per process.

Once these values setting in /opt/sun/messaging/sbin/configutil then imap server 
failed to start

imap server - log: 
[29/May/2006:17:44:37 +051800] usg197 imapd[6747]: General Critical: Not enough 
file descriptors to support 4000 sessions per process; Recommend ulimit -n 12851 
or 58 sessions per process.

fs.file-max = 65536

*   soft  nofile  65536  
*   hard  nofile  65536