Hello,
@LeFred
Seems like you can use a method similar to one described at
https://chase-seibert.github.io/blog/2005/10/19/postifx-header-based-routing.html
"First, enable header checks in /etc/postfix/main.cf:
header_checks = regexp:/etc/postfix/header_checks
Then, insert a new header check in /etc/postfix/header_checks:
/^X-Smarthost: (.*)$/ FILTER smtp:$1
This will use a regex to match any email with a "X-Smarthost:" token in the header, and save the substring in the parenthesis to $1, which you can conveniently pass to the smtp transport. Any email not matching this rule will go through the default transport, which in a clean install means regular old DNS + smtp."
The bloger uses the original Postfix' main.cf, but in Proxmox Mail Gateway you should use "templates", so that the config isn't overwritten by updates, it's described in the PMG docs:
https://pmg.proxmox.com/pmg-docs/pmg-admin-guide.html#pmgconfig_template_engine
Also, he uses X-Smarthost header, while you'll need X-OTP-code: true, of course. You probably won't need the $1, just a static transport.
You can use regexp: or pcre: patterns for matching.
The detailed docs on header_checks are at
https://www.postfix.org/header_checks.5.html
