I have a client that can no longer send email to cbeyond. She gets an error back
Myclients.domain.com #5.5.0 smtp;530 Authentication required
My client has their own exchange server and they are using Outlook as an exchange client.
I telnet to cbeyond on port 25 from the mail server, enter helo command and then mail from:firstname.lastname@example.org. I get back 530 authentication required
This only happens when sending to Cbeyond. Since the bounce back has my clients domain, they say it is not on their end.
According to the message logs in exchange
message routed and queued for remote deliuvery
started outbound transfer of message
non-delivered report (ndr) generated.
Since this is only a problem going to Cbeyond, I think it is on their end however they disagree.