OUTLOOK 2003 SP1 Sending error

Question: I have Outlook 2003 (Windows XP) and apparently when I try to send emails as small as 110KB, Outlook gets hung up in a processing stage and never sends the email. In fact it rejects or response the email as not sent. Occasionally a message from Symantec will appear indicating an error that the connection was lost with the server and that I should contact my ISP. Symantec's help Tech support Online, says "wait a few hours or contact the ISP support desk and try again. I have removed the programs re installed them and even was instructed to ensure the physical connection, the signal,(the cable) was only split once at 3.5 DB. I have attempted all and still the messages once they reach a certain size to do not send. Any thoughts or comments ? Thank you for any advice you may be able to offer.