* Fix issue with concatenating $dmarc_milter and $dkim_milter in main.cf
Upon each start the `smtpd_milters` and `non_smtpd_milters` would be extended with the following:
```
smtpd_milters = $dmarc_milter $dkim_milter
non_smtpd_milters = $dkim_milter
```
In my case they became long enough that mail delivery stopped. I think this was because of the extra headers that are added by these steps. (which in turn would cause the mail to be dropped)
* fix sed to work when the variables are there and when they are not.
---------
Co-authored-by: Georg Lauterbach <44545919+georglauterbach@users.noreply.github.com>
68c6f247a6