Prove you cannot send. Show *us* the complete error message.
Version of Windows?
Version of Outlook?
Type of e-mail account?
How you connect to the Internet (or the mail host)?
Did you really expect a detailed response with such an obviously
clueless question? No details in question begets no details or focus in
responses.
Usually you get one chance per potential respondent to elicit a reply
from them. If they skip your post because you gave them nothing to go
on (no details, no versions, no context), usually they will just move on
to the next post and never return to yours. Go read: