Using DCC with forwarding?

Rose, Bobby
Mon May 20 15:44:03 UTC 2002

We used to use aliases also, but started using LDAP which was much nicer
and cleaner, granted our ldap directory is AD and most our users are
Exchange, but I redid some of the sendmail m4s so that it would work
with AD and Exchange.  It's much easier to manage and redirect mail with
a LDAP enabled directory.

-----Original Message-----
From: Vernon Schryver [] 
Sent: Monday, May 20, 2002 11:15 AM
Subject: Re: Using DCC with forwarding?

> From: Gary Mills <mills@cc.UManitoba.CA>

> ... 
>   env_To: <shirley_dyck@UMANITOBA.CA>  
> dir=

How do you redirect mail?  When I try sending mail to another system via
an alias, addr is resolved to the name.  Only when I really relay do I
see addr not being resolved, and the mailer value = "esmtp". Perhaps
you're using something fancy like virtual users.

> I've been giving this item more thought.  Sendmail resolves each 
> envelope recipient address into a triple: mailer:host:user.  (It does 
> the same with the envelope sender, but the result is unreliable. 
> That's why sendmail uses the SMTP peer address to control relaying). 
> In the case of local addresses, the mailer is `local', and the host is

> empty.  For non-local addresses, the mailer is `esmtp', and both the 
> host and user fields are present.  Clearly, only local addresses need 
> per-recipient logs, because the mail server has no knowledge of or 
> control over users at other sites.

It might be interesting to switch to the new versions of the dcc_conf
file from homedir/dcc_conf (i.e. add DCCM_USERDIRS=userdirs) to see the
"dir=" value.

In other words, I think you can have per-recipient logs and whitelists
for distant users, although the directory names will be odd.

> If the other site is running DCC, as it is in my case, that site can 
> do the per-recipient logging.  I realize that having multiple 
> recipients complicates the SMTP processing.  In the example above, 
> some of them would be delivered locally on the main mail server, and 
> the rest would be relayed to the second server to be delivered there.

> With DCC doing rejection, I'd like to have the mail both rejected and 
> relayed on the main mail server, and then rejected on the second 
> server, with logging on both!  I suspect that that is impossible.

I think it is possible but has bad side effects, including
   - partial target double-counting in the DCC database, which would
     you to double your bulk threshold.
  - effectively running with `dccm -a DISCARD` for messages to addresses
     on both systems.
  - clogging your postmaster mailboxes with double-bounces.

Vernon Schryver
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