I cannot send emails from my outlook.com. I appear to be receiving mails ok.  Mails are showing in my sent box as if they have been sent but recipients are not receiving them. I have set Gmail to forward emails to outlook.com. This was working fine till about 5-days ago.

I can send from Gmail ok and they appear in my outlook.com inbox, I just can't send or reply from outlook.com although they are in the sent box?