I was getting spammy signups - more than 200 a day. Thankfully I don’t have a working, discoverable subscription form that isn’t bot-hardened.
I still don’t understand why spammy signups are a thing. What does anyone get out of it?
Anyway, my suggestion is a) make sure the ones that bounce are unsubscribed (your software should be doing that anyway); b) remove by hand the obvious ones (name937302@outlook or similar@gmail); c) check click rates if you think that’s useful, though it’s unlikely to be given many mail servers click links in emails to check them.
