You got this error message within a email but you can't fix that problem by yorself?
Please contact your email administrator (postmaster) or your email provider and send him this url. Your mail server is configured not properly!
The mailserver of the sender is corrupted.
The mailserver gives a incorrect hostname in the required HELO/EHLO greeting. Usually this depends from a non complete or non correct configuration of DNS and / or SMTP and/or your server is "abuse-ignorant".
- the hostname in HELO/EHLO is not related to the servers IP-address (required by RFC!)
- the senders server is not a MX for the domain foo.bar of the sender email@example.com and is no complete MX byself
- the servers MX has no required postmaster or at least abuse contact
- mail is spam