I periodically have issues sending mail on my iMac 27"

I receive an error message stating that:

'Cannot send mail using the server iCloud'

it continues on with:

'Connections to the server "p42-smtp.mail.me.com" on the default ports timed out.'

It doesn't happen for every email I try to send. It has only just now started (over the past couple of days) for some emails.