I attempted to email a client yesterday, and received the message shown below in reply. Your assistance in resolving this would be greatly appreciated!
Reporting-MTA: dns; mx.zohomail.com
Arrival-Date: Wed, 13 Jan 2021 08:57:52 -0800
Original-Recipient: rfc822; redacted@domain.com
Final-Recipient: rfc822; redacted@domain.com
Status: 550
Action: failed
Last-Attempt-Date: 13 Jan 2021 16:59:19 GMT
Diagnostic-Code: "JunkMail rejected - sender4-pp-o99.zoho.com [136.143.188.99]:25997 is in
an RBL: http://www.barracudanetworks.com/reputation/?pr=1&ip=136.143.188.99"