The error message you’re encountering indicates that the sending mail server is identifying itself with a .local domain, which is not considered a valid public domain name. As a result, many receiving servers will reject the connection. To resolve this issue, the sending server needs to be configured to use a Fully Qualified Domain Name (FQDN) that matches its public IP address.

When a mail server connects to another server to send an email, it introduces itself with a HELO command, which should contain a Fully Qualified Domain Name (FQDN). If the server identifies itself with a .local domain, it’s not considered a valid public domain name, and thus, many receiving servers will reject the connection.

To resolve this, the sending server needs to be configured to use an FQDN that matches its public IP address. This can typically be done by setting the FQDN on the send connector¹. Additionally, ensure that both the forward and reverse DNS records for the FQDN match the server’s public IP address¹.

If you have access to the server configuration, you can update the myhostname parameter in the mail server’s configuration file (for example, /etc/postfix/main.cf for Postfix) to reflect the correct FQDN² or make the required configuration changes if using Plesk³.

If you’re not the administrator of the sending server, or the sending server is not managed by O’Brien Media, you should contact the server’s admin and inform them of the misconfiguration so they can make the necessary changes.