I am receiving a notification of delay message to deliver – Delay reason: SMTP error from remote mail server after initial connection: 421 Downstream server error

I am sending some email to my staff or clients since Friday and having bounced back.

I don't know what is happening as I never had problem with Hotmail or something.

I am sending from another domain to outlook, live and hotmail domains.

My host said it's a microsoft problem and I had to contact them.

There's not way I can contact Microsoft other than posting here.

How can I solve that?

Thank you