I know nothing about sendmail or any other mail server. The only thing I can suggest is that you turn off your computer, unplug your modem and leave it powered off for a couple of minutes. Be sure that any other computers that connect to the same modem and any router you have are turned off, also. When you reconnect the power to your modem, let it take 3 or 4 minutes to run its set up and settle down before you boot up your computer.
If that doesn't work, search the threads here. There may be a solution that has been posted already. If you don't find one, start a new thread. Choose your title with care. If your title matches one already in the forums, you may not get as much attention.

-Merlin

thx dude.. appriciate it..

You're welcome. Is the problem resolved?

-Merlin

not yet.. but im going through all the solution and suggestion that i can find.. worst case is i would have to reinstall my fedora... n start over

I hope you find the solution.
Hmmmm.... have you tried connecting directly to your modem, bypassing the router, to see if you get the same results? It may be no different, but if it is better, you'll know that the problem is in the router's connection or configuration. --just a thought.

-Merlin

Tough luck on that.. im using a wireless modem router.. i have to live with that.. im not sure whats wrong but im sure its not the router.. because my friend's ibook can access the network fine.. maybe i did something wrong with my FC5.. thx for the suggestion...

I don't suppose your router-modem has an optional socket for a wire, does it?
I don't have enough knowledge of wireless connections to be of much help. Sorry. I think the problem would be in your wireless configuration, but how to adjust the configuration is not among the things I have learned.

-Merlin

dont worry.. it got wires.. 4 port router modem with wireless networking... my pc using one of the port.. while the wireless connectivity is for my laptop... im currently dissecting what ive done wrong during the installation.. if any.. and im constantly trying to reconfigure my network setting.. so right now im trying any suggestion that i can thanks a lot...