Why aren't my emails being sent?

On my hotmail, I can receive emails but when I send them I get a delivery failure email that the email can't be sent even if I'm sending the email to a valid address.
I can't from my iPhone or even my laptop& pc.

what's wrong with it?
how do I get my emails to send.

* I use hotmail to send emails. It's my main account.

sorry if it's the wrong category, its the closest.

Download the free scanner from http://malwarebytes.org and run the full scan. Your machine might be infected and sending spam, which could get your address blocked. Then check with hotmail to see if there's a block on you sending.

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