I think this feature was retired by default a while ago.
eBay briefly implemented a function to kind of replace it, where a buyer could post a public question and an email would be sent to selected sellers of that item, as well as previous buyers, prompting them to answer the question publicly, but it pretty much tanked as a feature (lots of people misunderstood what was happening, buyers would ask questions to the seller of that particular listing rather than a general Q about the item, but sometimes that seller wouldn't even be notified of the question, while members that eBay prompted to answer had even less clue what was going on half the time, many even thinking it was spam / scam email).
So that was removed fairly quickly, and nothing like it has really been implemented since.
