Hi Wietse thanks a lot for your hint :-) Deployed and first tests show it works as it should: changing 5xx to 4xx in case of NX domain for nexthop.
Cheers tobi Am 15.10.19 um 21:58 schrieb Wietse Venema: > Wietse Venema: >> Wietse Venema: >>> Tobi: >>>> I wonder if the following idea is somehow "do-able" in postfix. We have >>>> a fallback postfix instance which gets all mails that our scanners could >>>> not send to our customers target server. Now the fallback tries to >>>> submit those msg to our customers. Sometimes our customers do not know >>>> how to manage dns and delete an important record (like the a-rec for the >>>> target server). We do not manage their zones, that's done by themselves. >>>> >>>> Now we thought that it would be very nice if we could "tell" our >>>> fallback instance that in case of NXDomain in DNS lookup of a target >>>> server to return a DEFER (4xx) instead of a REJECT (5xx). >>>> I found soft_bounce parameter in the docs but that seems too wide, as we >>>> would only soft bounce in case of NXDomain results of target servers and >>>> not for any other reason. Is it possible to use smtp_dns_reply_filter to >>>> filter for NXDomain results and return a DEFER action? >> >> Of course Postfix can, it just isn't called smtp_dns_reply_filter >> >> Instead, use smtp_delivery_status_filter. >> >> The filter is invoked with a string of the form : >> >> enhanced-status-code SPACE explanatory-text >> >> For example: >> >> 5.4.4 Host or domain name not found. Name service error for... >> >> So the following could do the trick for your fallback relay host: >> >> /etc/postfix/main.cf: >> smtp_delivery_status_filter = pcre:/etc/postfix/fallback_status_filter > > Corrected text: The '5' needs to be outside the (). > > /etc/postfix/fallback_status_filter: > /^5(\S+\s+Host or domain name not found.+)/ 4$1 > > This changes the hard error into a soft one, and is more selective > than setting soft_bounce=yes. > > Wietse >>
