The new list software (Mailman3) differs from the previous (Mailman2) in that Web Accounts are distinct (but somewhat connected) with Subscriptions to mailing lists. While you don't actually need to register an account to have a subscription (and people who were transfered didn't get an account created) it is strongly suggested to have one, as it is needed to use the Web Interface to do things like looking/searching the archives, or adjjusting the settings of your subscription.

To subscribe to the list, go to https://lists.arlingtonlist.org and click on the "Sign Up" link in the upper right of the screen (in the blue bar at the top).

This will take you to the "Sign Up" page where you need to choose:

• A User Name: 
• Your Email Address
• A Password (and then repeated in the second box)

And press the blue "Sign Up" button at the bottom of the form.

If the User Name or EMail Address is already used (or connected to a request that is still pending) you will get an error.

The system wil then send a confirmation email to that address with a link to click on to confirm that this is your email address. If you don't see the message even after a few minutes, check carefully in your spam folder (or other place you system might put messages). GMail users, be sure to check the "alternate Inboxes" of GMail, as it might go there. If you really didn't get the message, your email system is blocking the list, and you will need to wait 3 days to try again, or you need to try a different email address.

There currently is a problem with Yahoo, and the domains it manages like AOL and Verizon, that it seems to have a habit of not accepting mail from the list.

After you have registered, your next step would be to create a subscription (unless you are already subscribed)

An additional point to make is that one "Account" can be connected to several email addresses. I think these allow posting to subscriptions to be from any of those addresses.