--- In postfix-us...@yahoogroups.com, Wiebe Cazemier <wiebe@...> wrote: > > Hi, > > I don't really know where to post feature ideas, but this seems the only > viable option. > > I was setting up a fallback MX server with Postfix and was struggling with > preventing backscatter mail. I thought I found a good solution, but it turned > out to be an illegal option. > > Postfix has the ability to do recipient address verification. When postfix > acts as a relay server, this prevents backscatter mail (bounces of messages > because the server that is relayed to doesn't accept the user). Backscatter > is usually caused by spam of course, because spam is sent to all kinds of > users @example.com. > > I had in mind to use recipient address verification to avoid that and then > set "unverified_recipient_tempfail_action = permit". The idea behind this > was: > > - Prevent backscatter mail when the primary host is up because every address > is verified first. > - Accept all mail when the primary host is down, so that incoming messages > aren't deferred. > > But permit is not a valid option for unverified_recipient_tempfail_action. > Would it be an idea to implement this? > > I know I can use permit_mx_backup and permit_mx_backup_networks, but I'd > rather not have to maintain a list of networks on the fallback server, partly > because I want to be a fallback server for servers that I don't maintain and > of which I have no idea if the address changes. > > Regards, > > Wiebe >
I'd like to chime in and add my support to this. Frankly, some of the obtuse replies to this reasonable feature request have been bordering on rude imho. I had a very similar problem to Wiebe last week when our primary mx started crashing because it could no longer communicate with our Dovecot SASL provider (dovecot had killed itself due to the system clock suddenly changing by 86 seconds, which itself was caused by a misconfigured ntp.conf file). While the primary was down, our secondary mx accepted mail for 3 of the domains it is configured to backup but all email to the fourth domain was deferred because it just so happened that the relevant entries in the verify_cache had expired shortly before the primary went down. The outage lasted about 4 hours but it would have been nice if senders hadn't received defferal messages and I could have simply flushed the backup queue to get the mail across once the primary was running again. Instead we had to wait for the affected sender MTAs to re-try delivery. unverified_recipient_tempfail_action = permit would have solved this problem with the small penalty of a brief period of potential backscatter. Where is the down side? Charlie
