[zaudo]

But it's much worse for the operator of the list to take actions which are invisible to the user. That's why I agree with mcv's point here. There is no perfect solution, someone will always be unhappy, but I think it's preferable to send an additional email to your user explaining "if you don't do X, then we will do Y".

They may well consider this email to be an annoyance, but I think that's better than making an assumption, taking an action and leaving users in the dark. Some will prefer that, but some will be confused about why your service isn't working for them.