If you don’t want to get the Groovy way, you could do it with a sh step.
The xmllint command would give you the result you’re expecting, and you could then use this result to trigger your email sending. xmllint is not installed by default, but if you’re using a Linux agent, it’s available for almost all architectures/Linux distros in the libxml2-utils package or equivalent.
I’m sure you can use HttpRequest, but you would have to use Groovy, which you wanted to avoid, am I right?
You could do everything with a bash script using curl and xmllint.