What it means and how to fix the message "rejected MAIL, Access denied - Invalid HELO name (See RFC2821 4.1.1.1)"
If in your email client (Outlook, Thunderbird, macOS Mail, etc.) you see the following message:
rejected MAIL, Access denied - Invalid HELO name (See RFC2821 4.1.1.1)
This is probably because an option called My outgoing server (SMTP) requires authentication is missing.
How to fix it in Outlook
Depending on the version and language, go to Tools → Accounts → Preferences → Servers. There activate the SMTP authentication option. If it asks for a username and password, write the full email address and password for that account.
Recommended readings
Still need help?
If this guide didn’t solve your issue, our team can help you via ticket.