Comment by froh

tooling and practice.

First you use a tool designed around following mailing lists. text based mail readers. they represent the threads in a compact form, allow to collapse threads and have them only resurrect if new content shows up. they also allow for pattern based tagging and highlighting of content "relevant to you", senders of interest, direct mentioning of your name/email address, ... and minor UX niceties like hiding duplicate subject in responses (Re: yadda <- we know that, it's at the top of the thread already)

such tool ergonomics allow you to focus on what's relevant to you

Hint: Outlook doesn't cut it.

And then with the right tool you practice, you learn how to skim the thread view like you maybe learned to skim the newspaper for relevant content.

and with the right tool and practice in place you can readily skim mailing lists during the day when you feel like it and can easily catch up after vacation.