Mail Connection Doctor say "iCloud SMTP account failed. Have made no changes to any of my settings. Why would this happen?

Have tried reconnecting and no joy. Tried cycling power and restarting Mac and no joy. Had the internet company try their thing and the system is working proper. Can access a gmail account, but can not send or receive emails. This started approximately 9 PM last night. No power surges or other reasons I can determine. Please help