Now I'm getting refused emails that I'm apparently sending to myself,
Apparently your myip## spams are now refused from me to me thru Mail Delivery Subsystem so I can't block this garbage.
1st
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Sounds like your account may be compromised. Here’s some tips to protect your account and to keep your information private and prevent unauthorized access to your account: https://help.yahoo.com/kb/new-mail-for-desktop/secure-yahoo-mail-account-sln2080.html