The mail user reports the error:

Task user@domain.com – Sending reported error (0x800CCC78): ‘Cannot send the 
message. Verify the email address in your account properties. The server 
responded: 550 Access denied – Invalid HELO name (See RFC2821 4.1.1.1)

Corresponding entry in Exim logs say:

2014-09-24 07:06:31 H=isp-ip-dom.net [xxx.xxx.xxx.xxx] rejected MAIL 
<user@domain.com>: Access denied - Invalid HELO name (See RFC2821 4.1.1.1)

At Bobcares help desk support services, this is a common error we see in DirectAdmin shared hosting servers. Strict anti-spam rules or lack of SMTP authentication usually cause this error.

Given below are a few scenarios we’ve encountered, and the solutions we provided for them. (more…)