[pfx] Re: header_checks sees original From: header despite s mtpd milter correction — execution order question

 
Thanks Victor,

Your statement that “header and body checks run first, then milters” is very clear, but the MILTER_README.html seems to suggest that processing occurs before queueing, and I had interpreted that as implying that milters run before cleanup/header_checks in the flow.

My understanding was consistent with the documentation in the sense that if I modify the From: header using header_checks, the milters would still see the original From: value rather than the modified one.

This is why I am a bit confused about the exact ordering and how cleanup, header_checks, and smtpd_milters interact internally.
In summary, I just want to confirm the precise order of execution between header_checks, smtpd_milters, and milter_header_checks, because depending on how it is interpreted, it can sometimes appear that one runs before the other or vice versa.
Thanks again for the clarification!

Pete


    On Monday, May 18, 2026 at 12:21:32 PM GMT+2, Pedro David Marco <[email protected]> wrote:  
 
 Hi,
I am trying to understand the exact execution order between header_checks/cleanup and smtpd_milters.
I have a custom milter that repairs invalid From: headers 
Example flow from logs:
1.- cleanup logs a header_checks warning on the original header From: <[email protected]>
2.- Then my milter replaces it with: From: <[email protected]>
3.- milter works ok, since postcat shows the corrected header in the queued message.
What confuses me is that according to my reading of MILTER_README, smtpd milters run before queuing, so I expected cleanup/header_checks to see the modified header rather than the original one. However, the log shows that cleanup sees [email protected] and not [email protected].
Am I misunderstanding how cleanup interacts with SMTP milters internally?
Thanks
Pete.

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