I tried to send an email to a developer to whom I've sent countless previous emails, and it bounced with this message. (I tried sending from two different Yahoo email accounts.)

Emails sent to myself at Yahoo and to my daughters at Gmail went through.

Who's doing what to my emails?

Thanks.
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The new Great Equalizer is the SEND button.

In Memory Of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire