users timed out connecting to mail box

i have installed ispconfig on a new server every thing seems to be working exept when the users connect from the internal lan they are timming out downloading there mail error Task '192.168.0.5 - Receiving' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP).' This is happening to all internal mail users. I am not sure where to look as new to linux my ping resalts to the internal card is 1ms. there does not seem to be erros in the mail log Can you help

 

And connecting from outside your LAN does work?
What are the outputs of

Code:

netstat -tap

and

Code:

iptables -L

?
Which distribution are you using?

 

thanks for the reply sorted problem out. iIt was a intermittent cable fault. Appertained the quick response