Rewrite From header in postfix
Posted by valqk on
The essential steps
Create /etc/postfix/header_checks (discussed below) then run these commands
cd /etc/postfix
postconf -e 'smtp_header_checks = regexp:/etc/postfix/header_checks'
/etc/init.d/postfix reload
Developing the header_checks file
Line format
For present purposes, each effective line of the header_checks file is of the form
/pattern/ REPLACE text...
The pattern
The /pattern/ is a POSIX regular expression matching the "FROM:" header. So it always begins with
/^From:
The pattern should always be anchored to the start of the line using ^. This ensures no false positives (such as matching "From:" in some other header such as the subject) and gives better postfix performance (postfix does not have to scan the whole of each header looking for the match).
The rest of the pattern depends on local requirements – what you want to match.
Any whitespace in the pattern should be represented by [[:space:]]. This avoids warnings from postmap such as "record is in "key: value" format; is this an alias file?" and "duplicate entry".
The text
display-name needs double quotes.
angle-addr needs the < and > characters.
Development techniques
To find out what's after the "From:":
If the regex matches, the original headers can be displayed by
grep -o 'replace: header .*$' /var/log/mail.info
Keep the original header text in the re-written header by using back-substitution in header_checks like (replace):
/^From:[[:space:]]+(.*)/ REPLACE From: ">${1}<"
Reference
Postfix Architecture Overview: http://www.postfix.org/OVERVIEW.html
Postfix Address Rewriting: http://www.postfix.org/ADDRESS_REWRITING_README.html
Postfix Lookup Table Overview: http://www.postfix.org/DATABASE_README.html
REGEXP_TABLE man page: http://www.postfix.org/regexp_table.5.html
header_checks man page: http://www.postfix.org/header_checks.5.html
Create /etc/postfix/header_checks (discussed below) then run these commands
cd /etc/postfix
postconf -e 'smtp_header_checks = regexp:/etc/postfix/header_checks'
/etc/init.d/postfix reload
Developing the header_checks file
Line format
For present purposes, each effective line of the header_checks file is of the form
/pattern/ REPLACE text...
The pattern
The /pattern/ is a POSIX regular expression matching the "FROM:" header. So it always begins with
/^From:
The pattern should always be anchored to the start of the line using ^. This ensures no false positives (such as matching "From:" in some other header such as the subject) and gives better postfix performance (postfix does not have to scan the whole of each header looking for the match).
The rest of the pattern depends on local requirements – what you want to match.
Any whitespace in the pattern should be represented by [[:space:]]. This avoids warnings from postmap such as "record is in "key: value" format; is this an alias file?" and "duplicate entry".
The text
display-name needs double quotes.
angle-addr needs the < and > characters.
Development techniques
To find out what's after the "From:":
If the regex matches, the original headers can be displayed by
grep -o 'replace: header .*$' /var/log/mail.info
Keep the original header text in the re-written header by using back-substitution in header_checks like (replace
/^From:[[:space:]]+(.*)/ REPLACE From: ">${1}<"
Reference
Postfix Architecture Overview: http://www.postfix.org/OVERVIEW.html
Postfix Address Rewriting: http://www.postfix.org/ADDRESS_REWRITING_README.html
Postfix Lookup Table Overview: http://www.postfix.org/DATABASE_README.html
REGEXP_TABLE man page: http://www.postfix.org/regexp_table.5.html
header_checks man page: http://www.postfix.org/header_checks.5.html