I'm trying to set up exim4 as a smarthost in front of the ISP mail server. Everything works fine, except from some emails coming from invalid senders (most likely spam). The ISP rejects them with
450 4.1.8 <firstname.lastname@example.org>: Sender address rejected: Domain not found
which causes the exim smarthost to retry, increasing the queue size unnecessarily.
The closest I managed to configure this was using
/etc/exim4/local_sender_callout file. But then the callout goes to the ISP, which then rejects it with
554 5.7.1 <email@example.com>: Relay access denied (for any address, even valid ones). Setting
/etc/exim4/passwd.client does not seem to work in this case...
How can I set up sender verification (with, or preferably without callout) with exim smarthost?
clarifiation: my exim is not an open relay, it does already specify only restricted list of domains it accepts emails for. Those emails are then sent to the smarthost for delivery to the actual mailboxes. A diagram of the set-up would probably look something like this.
Internet -> my exim(mx) -> ISP(smarthost) <- users accessing email via POP/IMAP
my domain's mx records point to my exim server. ISP however accepts emails for my domain and stores them in mailboxes.