I have a problem with my emails. (UBS.az).
Today I received mail from the postmaster.
Reason: There was an error while attempting to deliver your message with [Subject: "t 3"] to firstname.lastname@example.org. MTA p3plsmtpa07-05.prod.phx3.secureserver.net received this response from the destination host IP - 184.108.40.206 - 554 , 554 5.7.1 <p3plsmtpa07-05.prod.phx3.secureserver.net[220.127.116.11]>: Client host rejected: "Client hostname blocked.".
I think 18.104.22.168 your ap address is blocked
Please remove your mail is a block list