About 9 hours ago I got a massive number of disabled subscriptions (40-50) of aol.com addresses because of excessive bounces ~10h ago. Bounce notifications are mostly of the type:
SMTP error from remote mail server after MAIL FROM:<firstname.lastname@example.org> SIZE=16180:
host mx-aol.mail.gm0.yahoodns.net [22.214.171.124]: 421 4.7.0 [TSS04] Messages from 126.96.36.199 temporarily deferred due to user complaints - 188.8.131.52; see https://help.yahoo.com/kb/postmaster/SLN3434.html: retry timeout exceeded
Let me know if I can provide more detail. Mailing list in question is wikilovesmonuments but sounds like a more generic issue is at the core.