What I mean is passively let them take up the problem themselves if they want your newsletters. Since it's something they expect and want, they might choose to

What I mean is passively let them take up the problem themselves if they want your newsletters. Since it's something they expect and want, they might choose to pressure their email provider into solving it. Of course if they don't really want it or just half-heartedly signed up because it seemed like it might be useful at the time then they're not going to make the effort. And I guess that's the situation almost everybody is in when they find they're not receiving emails due to false positive spam filtering. So it's basically a terrible situation for everyone :( At least we have these magic solutions like MailChip or MailJet (what I use because the free plan fits my usage pattern) so you could turn to something like that if you really had no luck chasing the spam list company.