reject mails unknown users at smtp stage (postfix &relay_recipient_maps)

[Peter Russell]

Mikael Kermorgant wrote:
> 2007/2/7, Drew Burchett <DrewB at united-systems.com>:
>> You didn't mention what sort of backend you're delivering to, but here's
>> the way I did it with Exchange 2000 & 2003:
>>
>> Local_recipient_maps =
>> hash:/etc/postfix/db/local,ldap:/etc/postfix/ldap/users.ldap
>>
>> The file /etc/postfix/db/local contains a list of domains that I can
>> relay for, but can't be contacted via ldap.  This could also be a list
>> of individual users if you wanted to keep it synched with your list of
>> valid email addresses.
> 
> Thank you, that worked !
> Sorry for being offtopic, I suspected there would be something linked
> to postfix's configuration with the hold queue which is a bit
> mailscanner specific.
> 
> Regards,
> 

Any have any thoughts on performance difference between the method 
suggested by Drew Vs a local hashed recipient map?

I am concerned about the quality of the network connection from my GW to 
the Exchange - Exchange is unreachable is mail rejected or deferred?