ezmail | Easily send out many customised emails to your contacts | Email library

Well, this is because at the moment you add boolean operator !, your condition can no longer be Interpreted as Variable Expression. Instead it needs to be evaluated using language (javascript by default).

In other words, if you check the Interpret Condition as Variable Expression checkbox, condition is compared to word true - that's it! If you add exclamation mark in front of it, it will become !true and will fail.

You have several options:

• Uncheck Interpret Condition as Variable Expression, so that condition is evaluated using JavaScript. But as documentation states, there's a performance penalty for that.

• Reverse your Response Assertion condition, so that it fails when there's no need to send email. That way you keep If Controller to simple ${JMeterThread.last_sample_ok}

• You can also create custom variable in Http Request post-processor which will take a value opposite of assertion, but will evaluate to true or false. Use that variable in If Controller.