Been trying to send emails to previous clients however keep receiving the following error:

ERROR 550- UNDELIVERED MAIL

Original-Recipient: rfc822; ********@******
Final-Recipient: rfc822; ********@******
Status: 550
Action: failed
Last-Attempt-Date: 5 Apr 2023 10:07:52 GMT
Diagnostic-Code: rejected because your sender IP 136.143.188.56 is identified on the global
            threat intelligence network as a SPAM IP, Please contact your email
            administrator.

Original-Recipient: rfc822; anna.weylandt@weylandtshome.co.za
Final-Recipient: rfc822; anna.weylandt@weylandtshome.co.za
Status: 550
Action: failed
Last-Attempt-Date: 5 Apr 2023 10:07:52 GMT
Diagnostic-Code: rejected because your sender IP 136.143.188.56 is identified on the global
            threat intelligence network as a SPAM IP, Please contact your email
            administrator.

How can this be rectified as it is severely affecting our ability to conduct daily business operations