Mail servers have an SMTP authentication characteristic enabled in them, to validate customers who attempt to ship mails by way of that server.
The ‘SMTP AUTH’ error often occurs when customers attempt to ship mails with out correctly authenticating their mail account in electronic mail shoppers resembling Outlook or Thunderbird.
What causes the error ‘SMTP AUTH is required for message submission on port 587’ in cPanel/WHM servers
With the most recent cPanel/WHM replace, electronic mail accounts that had been working high-quality until now, could discover their mails getting undelivered, displaying this error message within the Exim log:
2016-09-22 04:28:29 H=(:1741 F= rejected RCPT : SMTP AUTH is required for message submission on port 587
This has occurred attributable to a contemporary safety characteristic carried out in cPanel/WHM – ‘SMTP AUTH’ requires SSL by default.
To fight spamming in servers and to supply safe electronic mail transmission, electronic mail shoppers that attempt to ship mails with out utilizing safe transmission shall be denied mail supply by way of the server.
The choice that determines that is ‘Require shoppers to attach with SSL or challenge the STARTTLS command earlier than they’re allowed to authenticate with the server’, which is about to ‘On’ by default, in WHM -> Exim Configuration Editor.
Whereas this SSL setting is enabled by default for SMTP, IMAP/POP3 stills works with out SSL. So servers with ‘POP earlier than SMTP’ characteristic enabled, is not going to face this error.
Nevertheless, as ‘POP earlier than SMTP’ characteristic authorizes customers to relay by way of the mail server, this setting is disabled in WHM for a lot of servers attributable to safety points:
Thus, customers in mail servers with the next mixed setting, will get error after they strive to sends mails with plain authentication:
1. POP earlier than SMTP – disabled
2. Require shoppers to attach with SSL – enabled
With these settings in place, SMTP authentication is not going to work except STARTTLS OR SSL/TLS is enabled in mail shopper.
The error can occur even within the case of mailer scripts or third celebration software program that ship mails from the server with out SSL authentication.
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The error message, nonetheless, varies with the port configured within the electronic mail shopper or code of the customers. For customers connecting to port 587 with out SSL, the message within the logs could be:
rejected RCPT : SMTP AUTH is required for message submission on port 587
For customers connecting to port 25 of mail server, here’s a variant of the error message from the Exim logs:
rejected RCPT : Please activate SMTP Authentication in your mail shopper. () [IPaddress]:1604 shouldn’t be permitted to relay by way of this server with out authentication.