Synology & Sendmail - I can not sign my mails with DKIM

Question

I post here as a last resort, I did not find the solution to my problem.

I installed optware on my Synology DS418 in order to have sendmail.

I send mail at the command line using the /opt/sbin/sendmail binary, the sendmail configuration is located in the /opt/etc/mail/ directory and the file is called sendmail.cf.

I modified the configuration of opendkim so that it listens on port 8891 as in the tutorial to install dkim on ubuntu.

You must then modify the configuration of sendmail to add the INPUT_MAIL_FILTER line ('opendkim ','S=inet:8891@localhost') in an .mc file and then use m4 to generate the configuration file.

But when I do that sendmail returns the following error:

unknown configuration line "INPUT_MAIL_FILTER ('opendkim', 'S=inet:8891@127.0.0.1')"

I did some research and came across the official sendmail site at http://www.sendmail.org/~ca/email/doc8.12/cf/m4/adding_mailfilters.html

This page explains that you need to define the filter in order to use it via the line:

define ('confINPUT_MAIL_FILTERS', 'opendkim')

But nothing helps I can not sign my emails and I always have the same mistake.

Help, if someone has already done this on a Synology his help would be really valuable.

Regards,

Olivier

I specify that with Roundcube it works, the signature dkim is good but not with sendmail.