Nowadays users needs tricks with RecipientIsRegex & SenderIsRegex for handling users of specific domains in a customized way in mailet processing. We need to provide utilities for avoiding such a hack.
In `mailet/standard` create two matchers (and their unit tests):
- SenderDomainIs will look at the envelope sender's domain. If equal to configured value, then all recipients will be returned. Overwise an empty list will be returned.
- RecipientDomainIs will return recipients mathcing a configured domain.
Please note that a valid domain needs to be configured, according to James core Domain model.