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

[Drew Burchett]

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.

The file /etc/postfix/ldap/users.ldap looks like this:

server_host = ip.of.my.exchange 
search_base = dc=my,dc=domain
bind_dn = cn=LDAP Query,ou=my.ou,dc=my,dc=domain
bind_pw = password
domain = hash:/etc/postfix/db/mydestination
query_filter = (|(mail=%s)(proxyAddresses=smtp:%s)) 
result_attribute = mail 
version = 3

Since I have multiple domains, I pointed the domain entry above to a
file that I also use for the mydestination entry in main.cf.

If I'm not mistaken, you could list multiple ldap files in your
local_recipient_maps, but keep in mind that each one is going to take
time to connect and query.  If you list too many, you may bring your
mail delivery to its knees.

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