I Would Like to Purpose an idea that when we create mailing lists, if we don't allow certain specified domains it could be more controlled from spams. Some times we need to get mails from different service providers only but not public, and it is hard to adding particular email mail address.
Example: if we are receiving mails from financials institution (Banks) some times they sending different information from different emails addresses.
Other Example: if we have Mailing Lists called "uitilitibills@domain.com"
mains we are getting mails from Cell Phone service Providers, Mails from Electric or power service providers, etc.....
But we don't want all public to be sending emails, 
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If possible to implement it will be highly appreciated