Empirically, modern mailing list services are spam senders
I still run a mailer on my office workstation, handling email to addresses that I've had for a very long time and which I used to use a lot in public (back in the days when the Internet was a much nicer place). To a very good approximation the only email that gets sent to it any more is spam.
(I have systematically transfered all legitimate email to other addresses elsewhere and I no longer subscribe to mailing lists and so on from it.)
Which leads to the punchline: I think I've gotten spam email sent to this machine by most if not all major providers of mailing list services. Many of them keep trying to send email to the machine over time, too.
This is what I mean when I say that empirically modern mailing list services are spam senders: they send spam. To me, from my particular vantage point, their spam sending activities outnumber their legitimate activities directed at me. These companies can protest all they want that they have plenty of legitimate customers too, but for me it is a ratio of all spam and no ham.
By the way, of course I don't bother to send complaints to these companies. It's a waste of time. From a global perspective sending complaints to these companies is what's called 'list washing'; I'll maybe get removed from this particular list or this particular spammer's collection of lists (because the spamming customer gets canceled) but they'll be back to sending me spam next week or next month or next year on behalf of the next spammer that they sign up. The only effective cure for me is to block them entirely, so that's what I do.
(I've touched on this issue before but not quite in these blunt terms. Extensions to the morality of running a mailing list service provider are left as an exercise for the reader.)
(This rant was sparked by a recent conversation with someone I know.)