Hello Sam,

I would like to ask you about setting SENDER=$FROM in user's mailfilter
file when SENDER variable is empty (please see
maildir_filter_saverules() function in maildir/maildirfilter.c file):

import SENDER
if ($SENDER eq "")
{
 SENDER=$FROM
}

Unfortunately, that maildrop filter code can be dangerous for a mail
server if a user has broken forward and he received a message from
empty <> address.

Recently we have had that situation in our mail system. Courier server
couldn't deliver a message to user's external account, so it was trying
to deliver DSN to our user, because the maildrop filter code has set
his internal address as a return address. The DSN message wasn't
delivered too, because user's forward didn't work, etc, etc. In result
we had looped DSNs from MAILDER-DAEMON...

I noticed it watching mail queue peak on our Munin graph. Fortunately
we have strong servers, so it wasn't noticeable for the rest our users.

So, my question is: why don't you set SENDER='[EMAIL PROTECTED]'
or SENDER='[EMAIL PROTECTED]' or something similar if SENDER
variable is empty?

In that case, if user's forward is broken, then Courier is trying
to deliver a DSN message to a postmaster, not to a user with not
working forward. I think it's reasonable solution, because information
about broken user's forward is valuable for mail system administrator.

What's your opinion?

My best regards,

Pawel

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