Mail Delivery Failed. WHY ?

[Albertwu]

I want to know if the issue is regarding the sender's mailserver or recipient's server ?

PHP Code:
This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

ulvyse.rbova@xxxx.com
host xxxx.com [217.17.97.20]
SMTP error from remote mail server after MAIL FROM:<info@zzzz.com> SIZE=1805:
550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

[aaronbrad]

In WHM panel go to Service Configuration > Exim Configuration Manager > Require RFC-compliant HELO and disable the same.

Try out the same.

[ikoula]

Hello,

I'd say smtp server (sender's mailserver) is rejecting the mail.

[VerdinaNET]

Are you using a FQDN as a hostname ? I've seen this before and that was the problem, give it a try.