Found my mistake.. that error is for su not zmdkimkeyutil -a -d

This now works properly and have created my DKIM.

Cheers

I have just started using Carbonio Zextras.

When running 

su - zextras /opt/zextras/libexec/zmdkimkeyutil -a -d mydomain.tld

I get:

su: invalid option -- 'a'
Try 'su --help' for more information.
root@mail:/tmp# su - zextras /opt/zextras/libexec/zmdkimkeyutil --help

Usage:
 su   [<user> ]

Change the effective user ID and group ID to that of <user>.
A mere - implies -l.  If <user> is not given, root is assumed.

Options:
 -m, -p, --preserve-environment      do not reset environment variables
 -w, --whitelist-environment <list>  don't reset specified variables

 -g, --group <group>             specify the primary group
 -G, --supp-group <group>        specify a supplemental group

 -, -l, --login                  make the shell a login shell
 -c, --command <command>         pass a single command to the shell with -c
 --session-command <command>     pass a single command to the shell with -c
                                   and do not create a new session
 -f, --fast                      pass -f to the shell (for csh or tcsh)
 -s, --shell <shell>             run <shell> if /etc/shells allows it
 -P, --pty                       create a new pseudo-terminal

 -h, --help                      display this help
 -V, --version                   display version

For more details see su(1).

Looks like there has been some changes or I have missed something.

Would like to generate our DKIM DNS entries for our domain. Any help appreciated!

Tanka