[Mimedefang] [slightly OT] MS Exchange server (was Re: virus notifications, etc.)

[alan premselaar]

On 3/27/03 10:56 AM, "David F. Skoll" <dfs at roaringpenguin.com> wrote:

[...snip...]
> Please see http://support.microsoft.com/default.aspx?scid=kb;en-us;304897
> for why this is rather difficult to do sensibly.  People running a
> proper mail server can use md_check_against_smtp_server in filter_recipient;
> people running M$ Exchange cannot.
> 

do you, or anyone else know of a way to change the Exchange Server's
behavior with regards to unknown users?  some sort of hidden option? a
registry that can be hacked? etc?

*OR* better yet. an opensource alternative that has the same functionality
and has multi-platform based client apps?
(then i can apply an ample amount of C4 to our Exchange server and fix it
for good)

> You may be able to hook into M$'s user-authentication scheme and write
> a filter_recipient routine that checks.  However, my guess is that only
> a few nonexistent users get the bulk of the spam or other unwanted mail;
> you can just write a special-purpose filter_recipient routine to catch
> those.
> 
actually, we have gotten quite a few <randomly generated
username>@domain.com types of spam and some dictionary attack type, as well.
(although recently that seems to have died down a little)

but what happens is, when an unknown user gets passed thru to the exchange
server, it tries to send an *actual* email saying "sorry, that user doesn't
exist", instead of bouncing it with a 554, and since the sender address is
forged, it bounces RIGHT BACK and causes a nasty mail-bounce loop until it
eventually times out.



thanks for all the assistance.

alan