Message-id header rewrite in exim

Some times it is advisable to change/hide some message headers in outgoing mail. For example, you don't like that helo string with your internal domain is shown in Received: header or when it appears in MUA's generated Message-id

Fixing Received header

Changes to Received header string can be made via received_header_text variable. This string is expanded each time it is used:

received_header_text = "Received: \
        ${if def:sender_rcvhost {from ${if match {$sender_rcvhost}{.*DOMAIN_PATTERN_HERE.*} {localhost}{$sender_rcvhost}}\n\t}\
        {${if def:sender_ident {from ${quote_local_part:$sender_ident} }}\
        ${if def:sender_helo_name {(helo=${if match {$sender_helo_name}{.*DOMAIN_PATTERN_HERE.*} {localhost}{$sender_helo_name}})\n\t}}}}\
        by $primary_hostname \
        ${if def:received_protocol {with $received_protocol}} \
        ${if def:tls_cipher {($tls_cipher)\n\t}}\
        id $message_id\
        ${if def:received_for {\n\tfor $received_for}}"

Fixing Message-id

To change Message-id i added system filter with the following contents:

#/etc/exim4/filter.conf

if not first_delivery then
 finish
endif

if error_message then
 finish
endif


if "${if def:h_Message-Id {yes}}" is yes and
    $h_Message-Id matches "@.*DOMAIN_PATTERN_HERE.*" then
        headers remove Message-Id
        headers add "Message-Id: <${message_id}@$primary_hostname>"
endif

This filter should be specified in exim's configuration with: