I run my own mail server + spam filter, so I'll chime in. I have seen a high uptick in spam making it to my inbox in the last two weeks. I primarily rely on Spamhaus blocklists + a Bayesian filter trained on old spam.
The uptick I have seen is going from 0-2 spams making it to my inbox to 10-20 spams making it to my inbox. When this has happened in the past, I have assumed it is spammers bypassing blocklists by finding new hosts, or by spammers finding a clever way to beat the filter. Usually after these big upticks, they drop off again suddenly, which makes me believe that it was a blocklist bypass and not a filter bypass (my filter is pretty weak and hasn't been retrained/updated in many years.)
Given all the news about hacks with self-hosted Exchange, more likely they're relaying through hosts with a built up trust... As good as Exchange + Outlook are as a user, it is pretty painful to see exploits in the wild like this.
The whole system just sucks as a whole, and feels too entrenched to come up with something better. Even a notify+pull system wouldn't fix these kinds of exploits, even if they would correct end-user breaches.
I use rspamd for my self-hosted mail and I still don't really see any spam at all. I've spent quite a bit of time tuning it (ensuring that domains I expect mail from are trusted, mostly) but I can't believe how GOOD it is.
The uptick I have seen is going from 0-2 spams making it to my inbox to 10-20 spams making it to my inbox. When this has happened in the past, I have assumed it is spammers bypassing blocklists by finding new hosts, or by spammers finding a clever way to beat the filter. Usually after these big upticks, they drop off again suddenly, which makes me believe that it was a blocklist bypass and not a filter bypass (my filter is pretty weak and hasn't been retrained/updated in many years.)