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Resolve a “HELO bug” error
This guide details the "bogus HELO" email error to help you avoid it.
When and Why Does This Error Occur?
To put it simply, the SMTP protocol (used for sending emails) has several phases, with the first one requiring the sender to announce who they are using a command called HELO, which must be followed by a valid address.
If you receive errors mentioning "bogus HELO," it means that some parameters (used by the person trying to send you an email or by the software you are trying to use) do not conform to the RFC ("Internet regulation"). This prevents the spread of viruses and spam.
For example, we reject any message from a mail server that would be called "server" instead of having a complete name like "server.domain.xyz" (= FQDN, "Fully Qualified Domain Name"). An IP address cannot simply define the server either. Examples of rejection:
The remote server's mail service has not been configured with a valid FQDN:
220 mta-gw1.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO 127.0.0.1or the mail server is not configured to use a real FQDN:
220 mta-gw1.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO [127.0.0.1]or the mail server is not configured to use a real FQDN:
220 mta-gw1.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO localhostor the mail server returns a host that is not in canonical form (FQDN):
220 mta-gw1.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO wwwor it is on a list of banned HELOs with us:
220 mta-gw1.infomaniak.ch ESMTP Infomaniak Network Mail Servers; HELO fakedomain.xyz
This will always result in an error:
250 mta-gw1.infomaniak.ch Hello, pleased to meet you MAIL FROM: user123@infomaniak.ch 250 2.1.0 user123@infomaniak.ch... Sender ok RCPT TO: user123@infomaniak.ch 550 5.7.1 user123@infomaniak.ch... Access denied - bogus HELO [1] ...