Email IP blacklisted. Problem sending email to client.

Email IP blacklisted. Problem sending email to client.

I am receiving the following error when trying to send emails.

xxxx@softech.com.pk INVALID_ADDRESS, ERROR_CODE :554, ERROR_CODE :5.7.1 Service unavailable; Client host [135.84.80.216] blocked using dnsbl.sorbs.net; Currently Sending Spam See: http://www.sorbs.net/lookup.shtml?135.84.80.216