Outgoing Mail on exchange 2003 flowing at a very slow rate

May someone please assist me:

My outgoing mail on exchange 2003 is moving out at very slow rates,you find that the intended recepient gets her email after 24hrs.
I can telnet into the smart host servers successfully,my configurations match those of the isp,i have disabled the antivirus ,but the problem persists therfore i have reanabled it.Dont know what the problem could be anymore.