Для exim нужно менять received_header_text, примерно как тут:
https://blog.regolit.com/2012/11/20/paranoid-outgo...received_header_text = Received: \
${if !def:authenticated_id \
{${if def:sender_rcvhost \
{from $sender_rcvhost\n\t} \
{${if def:sender_ident {from ${quote_local_part:$sender_ident} }}${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\
}}\
by $smtp_active_hostname \
${if def:received_protocol {with $received_protocol}} \
${if def:tls_cipher {($tls_cipher)\n\t}}\
(Exim $version_number)\n\t\
id $message_exim_id
