There are three solutions: (a) Digests; (b) Filtering into Folders; (c) Setting No Mail and reading on-line
With digests, you get a few big messages each day that contain all the messages for that day, instead of getting them as individual messages throughout the day. You enable digests by changing an option on your list subscription. See Digests for details.
With filtering into folders, you direct all List messages automatically into a specific mail folder on your computer, instead of having them interspersed throughout your general mail in-box. You set this up in a way specific to your mail client or service (AOL, Eudora, Outlook Express, Yahoo Mail, HotMail, etc). See Filtering for a bigger discussion on how to set up filtering, and Using the list with various programs for detailed instructions for you program (if a writeup is available for it).
There are advantages to each method, but filtering into folders is best, if you're willing to take a bit more trouble to set it up.
When you receive the list as digests, you can no longer treat each message as an individual e-mail for surgical deletion and other operations. Replying to a digest message works if you want to post a reply to the list, but the subject of the reply becomes something like "[arlington] RE: arlington digest, Vol 1 #318 - 28 msgs". It's easy enough to change that manually to the true subject, but if you forget, or type it wrong, your readers may not realize which message you are replying to. Also, with digests, there's no convenient way to reply to the sender rather than the whole List. You'll have to copy and paste the recipient's e-mail address, or use another method.
Filtering into folders automatically places all your Arlington List messages in a specific, segregated place (folder) on your own system or account, as soon as each message arrives. There are just as many messages and they arrive all day long, but they aren't cluttering up any other folder, and there aren't any other messages cluttering them up. You can go look at them in their special folder -- or not -- when you choose.
In their special ArlingtonList folder, you can still work with each message as an individual e-mail, and do things like sort and mark the headers, delete individual messages, and whatever features your e-mail system provides. Perhaps most important, you can reply or reply-all to an individual post in the usual way.
Another advantage of not using digests is that you can filter out messages from particular individuals, should you wish to. Again, the method for doing that varies with the mail system you are using.
There's essentially no discernable difference in efficiency between digests and filtering into folders: both take about the same time to download and both occupy about the same amount of disk space.