Configuring a Custom HELO Banner in Exim Print

Configuring a Custom HELO Banner in Exim

When assigning a dedicated IP address to a domain, it's crucial to properly configure the SMTP server’s HELO banner. If not correctly set, some recipients may reject your emails because many spam filters check the match between:

• the HELO banner name
• the IP address's reverse DNS (PTR record)

If these do not match, emails may be flagged as spam or refused entirely.

Verify configuration in WHM

Log in to WHM and ensure the following setting is enabled:

• Reference /etc/mailhelo for custom outgoing SMTP HELO

This option is located in the Exim Configuration Manager and must be set to ON to allow custom HELO banners.

Edit the /etc/mailhelo file

Once the feature is enabled, define a custom HELO banner for each domain by editing:

/etc/mailhelo

Use the following syntax:

yourdomain.tld:helo.hostname.tld

Example:

example.com:mail.example.com

Each line creates a mapping between a domain and the HELO name to be used for outgoing mail via its dedicated IP.

No Exim restart is required — changes take effect automatically.

Tip

Make sure the PTR record (reverse DNS) for the dedicated IP exactly matches the configured HELO banner. This consistency improves email deliverability and reduces the risk of being filtered as spam.