SMTP Error (550) (New Setup)

Hello
I am trying to setup the emails and followed the tutorials.
Also searched here only one question come up and that too I already did that.

I am not able to send emails except own domain, hotmail & gmail.
If I am trying to send it then getting this message.

SMTP Error (550): Failed to add recipient “email@mydomai.com” (No such recipient here).

Anyone can give me a hand!
Kind regards
Munish