Can't change the first header field and regarding ChangeHeader indices

[tdewolff]

It seems undocumented that the ChangeHeader index starts at 1 and not zero. When sending a mail such as:

From: foo1@domain.com
To: bar@domain.com
From foo2@domain.com

Message

• I can change To using: ChangeHeader(1, "To", "value")
• I can change the second From using: ChangeHeader(2, "From", "value")
• But I can't change the first From using: ChangeHeader(1, "From", "value"). Instead of changing it, it adds a new header field to the end of the header

This is regardless of whichever header field comes first, I simply can't change it. Might this be an issue with Postfix?

[tdewolff]

This is actually a bug in Postfix. You can circumvent the problem by issuing two modifications, first an insert at index=0, and then a chgheader at index=1 with empty value to delete the original. See https://www.mail-archive.com/postfix-users@postfix.org/msg101517.html