Specifying local users

Is RT meant to support the specification of RT users as recipients in forms by
specifying their username? If not, why not? It seems a pretty obvious feature
that most email systems support. If so, what’s the likely suspect for
it it being

I’ve been specifying RT users as recipients for some time, and it seemed to
work because most were local users. Recently, after assigning to some RT
users who don’t have local email accounts, much havoc has ensused…

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