PSA: check your yahoo mail forwarding settings
I had my yahoo mail forwarding enabled to my ex-employer 10 years ago - yeah pre gmail years when outlook ruled...
which yahoo disabled under the free plan some years back but the settings stayed intact.
Unbeknownst to me since Oct 8 Yahoo re-enabled the forwarding under the free plan and my emails were bouncing as they were getting forwarded to my ex-employer from 10 years ago. So check your yahoo forwarding settings!