Email won't send

So I can receive emails but they won't send and there is NO useful information anywhere to help as my problem seems unique.

My Apple ID was initially configured with my hotmail address which, after experiencing these problems, decided to change to my iCloud.me address. It hasn't helped. I continue to get, this message every time (I have also removed the Hotmail address from the SMTP server list):

The sender address *** was rejected by the server. The server response was: From address is not one of your addresses

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.

Sending from: #########

Even when I try to edit the SMTP Server settings, it still defaults to this message.

I can only assume there is some bug from a recent Software Update.

[Personal Information Edited by Moderator]