Using DCC with forwarding?

Vernon Schryver
Mon May 20 15:15:20 UTC 2002

> 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 force
     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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