Note:  In older versions of LISTSERV, list owners and other administrative "role" accounts (such as the LISTSERV maintainer) could not post to lists coded "Send= Private" unless their email address was subscribed to the list.  Current versions of LISTSERV allow these administrative "role" accounts to post even without a subscription, although of course the email address used must be the one associated with the administrative account.

I'm the list owner but I can't post to the list! Why not?

Ensure that the address from which you are posting is either listed in the list header as an Owner=, or that the address is subscribed to the list with posting privileges (e.g., the subscription is not set to NOPOST or REVIEW).  Note that your mail client or your outbound server may be changing your From: address slightly, which would prevent LISTSERV from identifying your mail as coming from the Owner= or subscribed address.  The best thing to do in a case like this is to ask the LISTSERV maintainer to check the LISTSERV system logs to see what happened when your posting arrived.

On my non-public list, I use (for instance) a Hotmail account as my Owner= address, and the Hotmail address is subscribed to the list and I get mail and can post just fine from that address. But I don't want to post from my list owner address, I want to post from my school address so that people don't think I'm the list owner. But I can't post from that address! Why can't I post? I'm the list owner!

(Yes, we really do get this question.) LISTSERV has no way to know that your Hotmail account and your school account belong to the same person (you) and therefore LISTSERV treats your school account just like anyone else's. You need either to subscribe your school address to the list or to make it an editor, depending on how you have the list set up.