slow uploads of large e-mail files

When sending large email(14,15meg)files it can take over a hour. The client is useing Verizon biz DSL. Verizon says that when sending the file starts and then stops, and have no idea why.
The OS is XP Pro w/SP2 Using Outlook 2002.
The client used to send the same size in less than 5 min.
Any help would be apprecieted