Re: [exim] Exim and sympa with DSN enabled lists

On 6 Jul 2022, at 10:24, Olaf Hopp (SCC) via Exim-users <exim-users@???> wrote:
> When DSN is switched off for a list sympa calls the exim with the args
> -oi -odi -oem -f test2-owner@??? -- my.name@???
> which runs fine. When DSN is enabled the args are
> -oi -odi -oem -N success,delay,failure -V00000031 -f bounce+my.name==a==example.com==test1==31@??? -- my.name@???
> which fails since "-N" means "This is a debugging option that inhibits delivery of a message at the transport level..."
>
> Is anybody using sympa with DSN enabled lists who can give a hint ?

Sympa wants Sendmail-compatible (and Postfix-compatible) DSN submission at the command line, which Exim can't support, so you must find or write a Sendmail-alike wrapper program or script that injects DSN-enabled messages via SMTP and configure Sympa to use it.

You have another problem, though. Sympa controls parallelism of submissions by using the -odi option. Tragically, Exim supports this just fine, but because it doesn’t support DSN submissions via the command line, and also doesn’t allow an SMTP listener daemon to use the -odi option (as Sendmail does), you’re powerless to perform synchronous deliveries of DSN-enabled messages, your best option being immediately queueing such messages and then running them from a queue with some limited number of (dynamically or pre-spawned) queue runners at some fixed low interval. (See main options remote_max_parallel and queue_run_max, and SMTP transport option serialize_hosts.) This comes at a regrettable cost to both latency and system load for polling for messages from the queue and starting enough runners to give good performance without abusing hosts. I humbly submit that Exim is really not the best choice in this (and similar “bulk mail”) situations, although if you want to, you can do it.

Cheers,
Sabahattin