Not all emails coming through, some being delayed for hrs, some come through

I recently built a new server for a client and installed the BIOS locked version of small business 2003.  I set up exchange and all user profile etc etc etc.  However since then emails are spiradic in terms of coming throug.  Some will arrive straight away, some wont at all and some come through hrs later but will no notification of any delay.  I am getting the following message on one users machine

task Microsoft exchange server error (0X8004010E). There are not enough system resources available for this type of operation

There is plenty of disk space and 4GB of RAM with a sytem managed paging file.  The clients mail does go through mail scanners but i have checked these entries and these are correct.  There is nothing relating to exchange in the windows logs

Any Help would be apreciated