Caching of domain dns/mx check

[la-ruby]

ValidEmail2::Address.new("[email protected]").valid_mx?  => false

the fact that ymail.con is not a valid domain, can the gem cache that fact?
during bulk checking of 1000 email addresses, that would avoid the need to make 1000 network requests.

[micke]

Great idea! A PR is most welcome!

[ianbayne]

Any thoughts on desired implementation for this, @micke? For example, a simple class-level cache using a class variable? Or something thread-safe like concurrent-ruby or Rails.cache (through requiring activesupport I guess)?