This guide details the "bogus HELO" email error to help you understand its origin and how to fix it.

When and why does this error occur?

The SMTP protocol (used for sending emails) involves several phases. The first phase involves the sender's server introducing itself to the recipient's server using the HELO command (or EHLO for extended SMTP). This command must be followed by a valid hostname.

If you receive an error mentioning "bogus HELO", it means that the identifier provided by the sending server does not comply with RFC 5321. This check is an essential security measure that helps filter out a large number of misconfigured servers, often used for distributing viruses and spam.

Infomaniak rejects any message originating from a server that identifies itself generically (e.g., "server") or locally. The server must use a FQDN (Fully Qualified Domain Name), meaning a complete and resolvable hostname of the type "server.domain.xyz".

Examples of configurations that will cause rejection:

Using a local or loopback IP address:

220 mta-gw.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO 127.0.0.1

Using an IP address enclosed in square brackets instead of a domain name:

220 mta-gw.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO [192.168.1.1]

Using an unqualified local hostname:

220 mta-gw.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO localhost 220 mta-gw.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO mon-serveur

Using a banned or obviously incorrect domain name:

220 mta-gw.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO fakedomain.xyz

In these cases, the SMTP transaction will fail with the following code:

MAIL FROM: user@domaine.com 250 2.1.0 user@domaine.com... Sender OK RCPT TO: destinataire@infomaniak.ch 550 5.7.1 destinataire@infomaniak.ch... Access denied - bogus HELO [1]

How to resolve this issue?

If you are using a programming script (PHP, Python, etc.) to send emails via SMTP, make sure that the library used is configured to send a valid domain name in the HELO command, and not the IP address of the web server.