Undelivered Mail Returned to Sender:BLOCKED

Undelivered Mail Returned to Sender:BLOCKED

Twice today I've tried sending an email to two different recipients and the emails are instantly being rejected and coming back with a message... email@address, ERROR_CODE :550, ERROR_CODE :permanent failure for one or more recipients (email@address:blocked) Reporting-MTA: dns; mx.zohomail.com Arrival-Date: Mon, 06 Jan 2020 12:56:03 -0800 Original-Recipient: rfc822; "name_of_person" <email@address> Final-Recipient: rfc822; email@address Status: 550 Action: failed Last-Attempt-Date: 6 Jan 2020 20:56:14 GMT Diagnostic-Code: email@address, ERROR_CODE :550, ERROR_CODE :permanent failure for one or more recipients (email@address:blocked) I've hidden the email address and name since this is a public forum, but did ZoHo just end up on a black IP list somewhere? I can't imagine it's on our end as this has happened twice today while manually sending email. Please help. Thanks.