I am using sendmail 8.15.2 and try to figure out how i could make an internal mailing list only accessible by internal users. This way i can create an allusers@domain.com and keep spammers away.
I read several topics but they are so old, i hope there would be an easier solution then adding a RULESET. I also tried adding the emailaddress in the Access file, but that made the mailbox unavailable for internal users also.
Other solutions like Postfix and Exchange support this option out of the box. In Exchange its even default setting. That makes me think it should be in Sendmail also.

The easiest way would be using an access database[1,2,3]. Mind you, I haven't used Sendmail in anger since the last century --- for good reasons. Thus, I can't tell you with certainty if the access database supports classless network filtering. On the other hand, uusing a mailing list manager would be more flexible and allow the security you want. Heck, even procmail+SmartList will do.

[1] http://www.tldp.org/LDP/nag2/x15291....DMAIL.ACCESSDB

[2] http://www.sendmail.org/~ca/email/do...html#access_db

[3] http://tldp.org/LDP/solrhe/Securing-...p22sec178.html

Forgot to add, I presume this server is for internal use only. If this is a SMB with only one server facing the wild internet, then I suggest you run sendmail in two containers, one external and another internal instance. Thus, you can relay from your external instance to your internal instance that handles your mailing list and other future organization-only lists you may need to create in the future.

The server is not only internal use, but there is another server in front with Postfix that checks for spam also (E.F.A.). If spam is send to the public address i will block it either by using a LOCAL_RULESET or let the first server block the spammers as that is its task.