[Exim] Quota on delivery to file

Hello,

I have several questions on quotas.

1. Is there any directive to set external quota checker?

2. If I set quota to 0 will it check for used space or just
deny all mail without checking?

3. If the first answer is 'no' then how can I notify
external program on any delivery attempt?

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Program source is just a special case of a patch

Andrey Novikov <novikov.web2000.ru> NAG-RIPN
Web2000 Ltd.