[exim] @example.net versus ""@example.net

Hello,

there is a strange difference in Exim's handling of empty local parts
»@example.net« and »""@???«:

mail from: <>
250 OK
rcpt to:<@example.net>
501 <@example.net>: no local part
rcpt to:<""@???>
250 Accepted

I would have expected that the latter address gives an "501 no local part"
as well. Is this intentional or a mistake?

Regards
    Michael