Mailing Lists vs. Email Handling

There is a major rewrite coming out for the email code.  I'm not sure when it will be deployed, but you may not want to spend too much time learning the details of the current system.
With that said, you don't actually need to configure an incoming mailbox for your list.  If you set the list type to "Allow posting only through this web site" then you can create a mailing list that can reach groups of people within your chorus based on roles or singing sections or other group memberships. You can then send email to everyone on that list by creating the message on the website using the "post" button for the list.
The incoming mailbox lets you create an email address somewhere and the Groupanizer server will poll that mailbox for messages and send them to the mailing list.  For example, I can create cool-kids@HeartOfMaryland.org and link that to a list that emails the entire bass section.  With that set up, any messages sent to the email address will go to my bass section.  This is nice because it lets us use email to reach groups of people instead of logging in to Groupanizer to create messages.  In practice, I have mailboxes set up for our frequently used lists and we just use the site for the infrequent lists because my email provider only allows me to create a limited number of mailboxes.
As I mentioned above, this is all changing at some point, so your best bet may be to just create the lists without the incoming mail for now because it is easier.  You can always change it later if you get impatient.