Any ESP that supports multiple mailing lists per customer lets you name your mailing lists. That’s useful for keeping track of where a list was from , but sometimes those list names are visible to the recipient:
Here the list name is visible on the opt-out / email preferences form, but you’ll also see them in (hidden) email headers or (visible) email footers.
“Last 10000″ is pretty innocuous, but I’ve seen “Non responders”, “Vegas blast”, “Opt-outs 2010″, “Jigsaw 3″, “Purchased 2011-07-01″, Trade 2″, “Co-reg 4″ as well as lists named after companies completely unrelated to the list owner.
You could check to see whether the list names are visible on every ESP and mail platform you use – or you could just assume they will be visible to end users eventually and be always careful in naming them.