Problems with sending mail

I have started getting the following message when trying to send an email

"You have exceeded your daily sending limits. See http://support.apple.com/kb/ht4863

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent."

I received this message yesterday and again today. The point is I have never sent 200 emails in one day - ever! I have iCloud as the SMTP server. I can feceive incoming mail. Any suggestions?