[Exim] Virtual domains

Hi

How can i make next thing with Exim: i have some virtual domains on machine
(@aaa @bbb @ccc) and i want that all mail that comes to user@aaa stores
at /var/spool/mail/aaa/user. And for other@aaa at /var/spool/mail/aaa/other,
for boss@bbb at /var/spool/mail/bbb/boss

But how?

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                Denis Chapligin