Сейчас у нас:

фронт-сервер: Exim 4.x

бек-сервер: Exchange  2003.

Проблема есть следующего плана: для того что бы выяснить, что получателя нет на сервере есть два выхода:

1. послать на exchange 2003, он проверит у себя и даст отлуп. сейчас организована эта схема.

2. отправить LDAP запрос с Exim на контроллер домена и отправить отлуп еще на стадии коннекта. Это предпочтительный способ.

Думал о пробросе почты совсем напрямую на exchange, и вот что нашел в мейллистах:

here was a recent thread about this on the exim-users mailing list. Some answers to the question, "What is the purpose of [using exim as a relay]?" Responses:

• exchange has a lot of security issues, keeping it isolated is a _good_ thing
• exim can be configured to be much more robust virus/spam filter, or just a second layer virus checker
• Exchange can be hard (if not impossible) to completely secure against hacking/DOS
• Exchange does not offer the level of access control, filtering, etc. that Exim does, leading to more junk mail being accepted
• Exchange is not entirely RFC-compliant and occasionally has trouble accepting legitimate mail from senders that expect full compliance.
• Exchange 2000 still does not have reasonable email address management tools for business. The "Recipient Policies" application of addresses is overhead which does not provide the promised flexibility, IMO. The most damning issues come down to the fact that it is easiest, in Exchange, to administrate a compllicated email address ruleset by proliferating mailboxes, which equates to buying more licenses. Using Exim as a hub allows Exchange to do what it was designed to do: permit each mailbox to have one and only one email address.

 Вот думаю теперь, пугаться или нет?