On Wed, Jan 08, 2014 at 05:31:37PM -0500, Wietse Venema wrote: > Postfix already has a feature that substitutes remote SMTP server > replies (smtp_reply_filter). > > Maybe it's possible to implement a similar substitution for DNS > server responses. If we want to use a regexp-based approach that > requires a conversion from DNS reply to text. The text is then > transformed by the filter, and then converted back to DNS response. > > I'm not recommending we do DNS -> XML + XPATH -> DNS.
I'd prefer to not go there at this time. The OP can put the hostname in question into /etc/hosts, and update that via periodic DNS lookups (which are NOPs when they fail). Then use a transport with smtp_host_lookup=native. This would work quite well if the C-library supports multiple A records for the same name in /etc/hosts as with say various Linux systems that have: $ cat /etc/host.conf multi on An hourly cron job can keep the hosts entries for the fragile CNAME up to date. -- Viktor.