1. Download DKIM proxy
wget http://downloads.sourceforge.net/dkimproxy/dkimproxy-1.3.tar.gz
perl -MCPAN -e'CPAN::Shell->install("Net::Server")'
perl -MCPAN -e'CPAN::Shell->install("Mail::DKIM")'
perl -MCPAN -e'CPAN::Shell->install("Mail::DKIM")'
tar -zxvf dkimproxy-1.3.tar.gz
./configure --prefix=/usr/local/dkimproxy
make install
2. Generate Public and Private Key
Generate a private/public key pair using OpenSSL:
openssl genrsa -out private.key 1024
openssl rsa -in private.key -pubout -out public.key
3. Pick a selector name... e.g. relay1 and from pulic key create following TXT record.
relay1._domainkey.domain.com. IN TXT "k=rsa; t=s; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDA2f/pF8NaHEEWNWIWNWL4H0gFJWici2nq3zyd3yw8K2/0ZxA8UTz72P67c7zTrMbEGL2Af6qFqY7N+Az8vO9/2uA3PrPJyrVW36KesGR2BJ3n8gvD+0XLzgaPP5clbrBWRyH/MHTETVB4G8SUH1LS++/KAlxbW4vGZuCP+lUGwwIDAQAB"
4. Create User dkim
useradd dkim
6. edit master.cf add following entry
submission inet n - n - - smtpd
-o smtpd_etrn_restrictions=reject
-o smtpd_sasl_auth_enable=yes
-o content_filter=dksign:[127.0.0.1]:10027
-o receive_override_options=no_address_mappings
-o smtpd_recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject
#
# specify the location of the DKIM signing proxy
# Note: we allow "4" simultaneous deliveries here; high-volume sites may
# want a number higher than 4.
# Note: the smtp_discard_ehlo_keywords option requires Postfix 2.2 or
# better. Leave it off if your version does not support it.
#
dksign unix - - n - 4 smtp
-o smtp_send_xforward_command=yes
-o smtp_discard_ehlo_keywords=8bitmime,starttls
#
# service for accepting messages FROM the DKIM signing proxy
#
127.0.0.1:10028 inet n - n - 10 smtpd
-o content_filter=
-o receive_override_options=no_unknown_recipient_checks,no_header_body_checks
-o smtpd_helo_restrictions=
-o smtpd_client_restrictions=
-o smtpd_sender_restrictions=
-o smtpd_recipient_restrictions=permit_mynetworks,reject
-o mynetworks=127.0.0.0/8
-o smtpd_authorized_xforward_hosts=127.0.0.0/8
7. Start Postfix
/usr/sbin/postfix-out-out/postfix-out -c /etc/postfix-out-out start
8. Start DKIM Proxy
/usr/local/dkimproxy/bin/dkimproxy.out --user=dkim --group=dkim --selector=relay1 --keyfile=/var/db/domainkeys/private.key --listen=127.0.0.1:10027 --relay=127.0.0.1:10028 --method=simple --domain=in.com --signature=domainkeys --signature=dkim --daemonize
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