This article is from the eBay FAQ, by William B. Shaw firstname.lastname@example.org with numerous contributions by others.
If eBay receives a complaint that your email address is no longer valid,
they will send a test message. If they confirm your address, nothing
happens. If the message bounces, your account is automatically cancelled
until you register a new email address and request to have it reinstated.
Invalid email addresses can be reported to safe harbor.