[Mailman-Users] dkim for several mailman lists on one server

[csa at web-analysts.net]

Ubuntu 16, Mailman 2.1.20, postfix 3.1.0

I'm running several mailing lists each with a virtual domain. I set up DKIM
for lists.domainname.tld but am getting DKIM signature missing at
https://dkimvalidator.com . It's saying it wants a DKIM for
hostname.domainname.tld. When I look at the mail log I see entries like this

Apr 19 07:49:42 hostname opendkim[1738]: 091CE1205AE: s=ppsdkim d=ucsf.edu
SSL error:04091068:rsa routines:INT_RSA_VERIFY:bad signature

Apr 24 09:25:31 hostname opendkim[1738]: 3B7CA120431: s=mail
d=domainname.tld SSL error:04091068:rsa routines:INT_RSA_VERIFY:bad
signature

Lastly, I'm confused by the term in the Mailman interface of  ' host_name'
where it says

host_name (general): Host name this list prefers for email.

The "host_name" is the preferred name for email to mailman-related addresses
on this host, and generally should be the mail host's exchanger address, if
any. This setting can be useful for selecting among alternative names of a
host that has multiple addresses.

Is the host-name literal for my server? Right now I have it set at
lists.domainname.tld. Is that incorrect?

Finally, my mailing list distribution success is mixed. Some users get them,
while others do not.

Thank you.

Christian