I am sorry you are having a problem with Yahoo mail. When you say it is slow to send are you using a email program or the webpage. Do you mean it is slow to arrive at the destination? Please would you expand?
Thanks for getting back, it is possible for it to be an internet problem but it is looking good from here at the moment. Are you using a wireless connection, when Yahoo goes slow are you able to browse normally?
What browser are you using? It may be worth trying another one such as Google Chrome or Firefox to see how that goes?