Groovy would be the most "batteries included" JVM language I think ... latest version even bundled YAML support in the standard library. Of course, it has all the downsides of a "kitchen sink" approach to language design.

Java has substantial industry backing, but you cannot argue that it has a battery-included standard library.

But to answer the question: yes, Go has support for SMTP in net/smtp and a lot of different serialization formats in encoding/

You can browse it all here: https://pkg.go.dev/std