FreeLists automatically unsubscribes subscribers who bounce continuously and you're notified of this in periodic activity reports (and you'll receive copies of these bounces if you turn on the CCERRORS flag) but subscribers can be removed by FreeLists without your knowledge for other administrative reasons.
In some rare cases a subscriber might contact us directly asking to be unsubscribed. Rather than direct them through the proper automated process we'll just handle that for them.
More commonly if silent unsubscribes are happening it's because of a Feedback Loop (FBL).
You might notice this in particular with AOL/Yahoo/Verizon subscribers. They're all managed with the same email infrastructure and their FBL is better than most – it's actually actionable.
Feedback reports happen when a subscriber marks a post as SPAM or Junk. The email provider sends us a per-subscriber report of the action. When a subscriber reports spam we have to act – we have to assume they don't want to receive mail from us – so they're removed (and banned!) to prevent further abuse. If we continue to send to a subscriber who's reporting spam there's a good likelihood the algorithms on yahoo's side will react by blocking all mail from a list, or even from FreeLists altogether.
If a subscriber is reporting they're trying to subscribe but they've been banned, this is probably what's happened. We'll have to fix it manually so please email us the subscriber's info.
Yes, but only through education and proper subscriber behavior. DON'T report posts to your list as SPAM, this is bad for your list and bad for our email sending reputation, and we have to respond by assuming it wasn't a mistake.
We assume that at least in the majority of cases subscribers reporting SPAM don't want to hear from us. There might be dozens or hundreds of these reports made per day and we're unable to handle the claims of “I didn't do it” or “oops! please add me back onto the list.”