This article explains what a HELO entry is and how to configure it.
When sending an email, the HELO is transmitted to the receiving server during the connection setup so that the receiving server can identify the sending server.
General Information on Configuration
Many receiving servers expect a correctly configured HELO. Generic entries such as localhost.localdomain or localhost can lead to rejection of your emails.
Generic HELO entries are a typical characteristic for incompletely configured systems. Likewise, constantly changing HELO entries can lead to being added to block lists.
The HELO entry should be a fully qualified domain name (FQDN) such as mail.example.org.
Ideally, use the (sub)domain of your server. If this is not possible, use your own domain as HELO.
Configuring the HELO Entry in Linux
Connect to your server via SSH and enter the server mail name:
$ sudo echo 'mail.example.org' > /etc/mailname
Additional Step for Postfix and Plesk
Plesk uses Postfix as its MTA by default. The configuration for Plesk and Postfix is therefore identical.
On the Linux shell, run the following command to change the changes to the Postfix configuration file (/etc/postfix/main.cf) directly:
$ postconf -e myhostname=mail.example.org
To load the new Postfix configuration, type the following command:
$ sudo postfix reload
Additional information can also be found on the websites of the respective software providers: