I have run into a problem described in section Sendmail REWRITING FEATURES on http://www.opendkim.org/README:
Due to the way the milter protocol is incorporated into the MTA, opendkim sees the headers before they are modified as required by those two features (MASQUERADE_AS and FEATURE(genericstable)). This means the DKIM signature is generated based on the headers originally injected by the mail client and not on the headers which are actually sent out by the MTA. As a result, the verifying agent at the receiver's side will be unable to verify the signature as the signed data and the received data don't match.
The suggested solutions to this problem are:
(1) Send mail with the headers already written as needed, obviating the need for these features (or just turn them off).
(2) Have two MTAs set up, either on separate boxes or on the same box. The first MTA should do all of the rewriting (i.e. use these two features) and the second one should use opendkim to add the signature and do no rewriting at all.
(3) Have multiple DaemonPortOptions lines in your configuration file. The first daemon port (port 25) does the header rewriting and then routes the message to the second port; the latter does no rewriting but does the signing and then sends the message on its way.
Since I'm not an expert in Sendmail I have configured it with help of online tutorials and used masquerade to remove host from email address (to get an address to look like user@domain instead of firstname.lastname@example.org). Due to same reason (not being an expert), I have problems understanding suggestions above.
Main question: What is the most elegant way to achieve host removal from email address without breaking OpenDKIM?
First of all, I'm so stupid!
As my colleague suggested, from field can be set by mail user agents to exclude host from email address.
I tried it and of course it works and I don't need masquerading nor genericstable.