disconnects after sleep, how can i prevent this?



i'm on an adsl internet connection, and is online all the time so to speak. The strange thing is that when i wake my Mac from sleep there is a little lightning icon or flash icon right beside the inbox indicating that has lost connection to the mail server i guess. The whole thing is fixed by clicking on the lightning icon, then you can check your mail again. Thing is that i don't want to loose the connection to my mail server, is there a way to keep connected even after sleep?

My system:

933 mhz g4 (quicksilver)
adsl (allways connected, no logins)
mac os 10.4.2