How to fix ‘SMTP AUTH is required for message submission on port 587’ error in cPanel/WHM servers
Mail servers have an SMTP authentication feature enabled in them, to validate users who try to send mails through that server.
The ‘SMTP AUTH’ error usually happens when users try to send mails without properly authenticating their mail account in email clients such as Outlook or Thunderbird.
What causes the error ‘SMTP AUTH is required for message submission on port 587’ in cPanel/WHM servers
To combat spamming in servers and to provide secure email transmission, email clients that try to send mails without using secure transmission will be denied mail delivery through the server.
The option that determines this is ‘Require clients to connect with SSL or issue the STARTTLS command before they are allowed to authenticate with the server’, which is set to ‘On’ by default, in WHM -> Exim Configuration Editor.
