Rejecting Mail at RCPT

[Spicer, Kevin]

Raymond Dijkxhoorn wrote:
> Hi!
> 
>> Does anybody know of a way to get Sendmail to check with a remote
>> SMTP server to see if a user is valid at the RCPT TO:?
>> At my site, a good portion of the spam we get is to invalid users.
>> If i can get Sendmail to check with the Remote SMTP server
>> before it queues it, that would reduce the amount of spam on my site
>> by at least 30%!
> 
> Put your users in LDAP and check with LDAP on your frontend servers.
> 
Does anyone whether its possible to check against Active Directory (it is LDAP after all)?  I tried once and failed - and never had the time to pursue it.  If so, is there a howto anywhere?