Add an email domain blacklist/whitelist to prevent proprietary info leaks in notifications

[jeffrey.yoder@…]

For organizations potentially dealing with proprietary information within their tickets, it is necessary to be able to block notification emails outside designated domains. Otherwise a user could inadvertently (or not) include a Cc to an email address that would leak proprietary information to non-need-to-know persons.

I tried using the admit_domains attribute in the trac.ini [notifications] section to no avail. rjollos responded to me in the trac-users Google group that this doesn't appear to be the intent of the admit_domains attribute and suggested submitting this for possible consideration as a future enhancement.