public PolicyCondition withStringExpression(IngressStringExpression stringExpression) {
        setStringExpression(stringExpression);
        return this;
    }
<p>
This represents a string based condition matching on the incoming mail. It performs the string operation
configured in 'Operator' and evaluates the 'Protocol' object against the 'Value'.
</p>

@param stringExpression
       This represents a string based condition matching on the incoming mail. It performs the string operation
       configured in 'Operator' and evaluates the 'Protocol' object against the 'Value'.
@return Returns a reference to this object so that method calls can be chained together.
aws-java-sdk-mailmanager/src/main/java/com/amazonaws/services/mailmanager/model/PolicyCondition.java