On my windows NiFi server , I am able to send unauthenticated emails using PutEmail processor by supplying SMTP Host name, Port 25 and user credentials. But in the email subject starts with UNVERIFIED SENDER.
but when I tried with port 587 which we are using for authenticated emails , I am getting the below error.
I am able to send emails using port 587 using PowerShell command. so i know the user has permissions to send emails on that port.