If you tried to send an email and got back a bounce message that said something like "HELO/EHLO argument invalid" here are the steps you can take:
- Contact your email administrator. You should have an administrator if you’re using Gmail for a work, school, or organization account. Otherwise, you can contact your email provider.
- Ask your administrator to send the fully-qualified domain name or IP address of the sending server when contacting Gmail servers.
This error usually comes up with devices like printers, scanners, and fax machines that also send mail.
Advanced information about HELO/EHLO
The HELO/EHLO error means that the mail server sending to Google has identified itself with an invalid value.
When mail servers talk to each other, they're required to identify themselves to the receiving server via a HELO or EHLO command. This identification should be the sending machine's fully-qualified domain name (like mail.example.com), or if that’s not available, its IP address. Any other value is considered invalid and may cause your email to be rejected.
For more information, you can refer to RFC 5321, section 4.1.1.1.
Example error
501 5.5.4 Empty HELO/EHLO argument not allowed, closing connection.
501 5.5.4 https://support.google.com/mail/?p=helo
501 5.5.4 HELO/EHLO argument "..." invalid, closing connection.
501 5.5.4 https://support.google.com/mail/?p=helo