I have a small content filter in my very basic Postfix installation. The content filter is a proxy based on smtpprox[1] that modifies the message content (the DATA part of the message). Postfix and the filter are on different hosts. I found smtpprox via a link on the smtpd_proxy_readme page.
[1] https://github.com/jnorell/smtpprox Like this: msg --> postfix(25) --> filter(25) --> postfix(10025) --> mailbox It works fine if I send a test directly to the filter... the filter connects to Postfix and the message is delivered. However, if I send to Postfix, which sends into the filter as a configured content_filter, then the inbound connection from the filter back into Postfix is blocked by the error message: warning: host filter[172.18.0.6]:25 replied to HELO/EHLO with my own hostname mail.example.com and the message is bounced. The way smtpprox works is that, excepting my modifications to DATA, it forwards whatever its source sends on to its destination. So the HELO 250 reply sent by Postfix to the filter is exactly what the filter sends back to Postfix. I've modified the filter to alter the HELO response so that this situation does not arise. I just wondered if I've missed something. Is there is a Postfix configuration setting that would disable this check? I looked, read the docs and also checked the source, but could not find one. smtp_proto.c#437 smtp_proto.c#551 Is it possible to disable this check on my filtered smtpd ?
