Intermittent error for sending the email from Katalon

Hi All,
I am able to send test mail from katalon and able to receive the auto triggered mail after the test suite execution as well however intermittently it gives error with same set of configuration.

Its like 1st time it will be success mail and second time when you do send test mail than it gives the error of unable to send the mail with the given configuration. I am using TLS protocol with port 25.
kindly assist if anyone else facing the same issue and is there any work around for the same.