This error occur when robot trying to send email message to client internal distribution group.
Robot using client server host. The email message send succesfully to external recipient but internal recipient does not receive the email message from robot.
Please check port and address of SMTP connection.
Already check. Port and address of SMTP connection is correct but the email still cannot pass through recipient inbox.
I felt like issue with SMTP connection only. Try with Outlook activity if you have outlook installed in that machine.
Will try it. Thanks.