Comment 0 for bug 1218335

Following the guide at https://help.ubuntu.com/community/Postfix/DKIM
will make opendkim sign the message two times, if you already have postfix use amavis.

To the core of the issue, postfix will use the (opendkim)milter before handing the message to the amavis. Then when amavis puts it back in the postfix queue and postfix will send it to the (opendkim)milter for a 2nd signature before delivering it.

Solution add a notice under common error and fixes for others that might have the same issue with Postfix\opendkim doublesigning when also using amavis.

One way to correct it is adding the no_milters parameter to the list of receive_override_options when putting the message back in the postfix queue. That is done in the postfix main.cf

snippet: /etc/postfix/main.cf -

127.0.0.1:10025 inet n - - - - smtpd
        -o content_filter=
        -o local_recipient_maps=
        -o relay_recipient_maps=
        -o smtpd_restriction_classes=
        -o smtpd_delay_reject=no
        -o smtpd_client_restrictions=permit_mynetworks,reject
        -o smtpd_helo_restrictions=
        -o smtpd_sender_restrictions=
        -o smtpd_recipient_restrictions=permit_mynetworks,reject
        -o smtpd_data_restrictions=reject_unauth_pipelining
        -o smtpd_end_of_data_restrictions=
        -o mynetworks=127.0.0.0/8
        -o smtpd_error_sleep_time=0
        -o smtpd_soft_error_limit=1001
        -o smtpd_hard_error_limit=1000
        -o smtpd_client_connection_count_limit=0
        -o smtpd_client_connection_rate_limit=0
        -o receive_override_options=no_header_body_checks,no_unknown_recipient_checks, no_milters

Reson for putting it under this article, cause many newcomers believes it is the issue of postfix\opendkim settings and not the way you feed messages back to queue from amavis.