Outgoing mails are blocked

Outgoing mails are blocked at info@naturenurture.lk which I used for sending some automated emails.

Also getting this error

{ [Error: Invalid login: 554 5.1.8 Sender Address Blocked]

code: 'EAUTH',

response: '554 5.1.8 Sender Address Blocked',

responseCode: 554,

command: 'AUTH PLAIN' }

How can I increase the limit.

Thanks