@WhiteCar wrote:
This requires a PTR entry to be made for the reverse DNS but this is not something I can do, it us under Vodafone's control.
If my static IP address is anything to go by, a PTR record already exists. You can verify yours by running
dig -x addr
where addr is your static IP address.
The HELO (or EHLO) command used by mail servers to establish a session with each other has the format
HELO fqdn
where fqdn is the fully qualified domain name for your IP address, the one reported by dig earlier. It is not the domain name in your email address.
To remove the error you are seeing, you need to configure your mail server so that it uses the correct string for fqdn. Most servers will default to the hostname which will almost certainly be wrong for machines sitting behind a NAT router. You will need to override it manually. For example, on the postfix mail server on linux, the value is controlled by the smtp_helo_name parameter in main.cf. Check the documentation for your mail server.
Hope this helps.
