email builder:
> some smtpd_*_restrictions checks. It turns out (from my testing, but I can't
> find this in the docs) that you can still use PREPEND to add a header even
> though you're looking at certain envelope data.
ACCESS(5) ACCESS(5)
NAME
access - Postfix SMTP server access table
...
PREPEND headername: headervalue
Prepend the specified message header to the message. When more
than one PREPEND action executes, the first prepended header
appears before the second etc. prepended header.
Note: this action must execute before the message content is
received; it cannot execute in the context of
smtpd_end_of_data_restrictions.
This feature is available in Postfix 2.1 and later.
