My client is receiving the following error. Please advise what needs to be done to allow the computer to send mail through. This is the only server blocking our mail. Thank you.
Reporting-MTA: dns; mail.akt3.com
X-Postfix-Sender: rfc822; firstname.lastname@example.org
Arrival-Date: Sun, 7 Jul 2019 10:35:43 -0400 (EDT)
Final-Recipient: rfc822; email@example.com
Remote-MTA: dns; d10023b.ess.barracudanetworks.com
Diagnostic-Code: smtp; 550 permanent failure for one or more recipients