Hmm, the problem still exists.
I'm getting mails from 2 months ago every day.
Obviously only a few people are having this bug, but it would be nice, if this could be solved although.
this has been a long term problem that started with season 3's release. there has already been several other threads on the subject and it was mentioned in one of the engineering reports as being Under Investigation.
i'd suggest that you submit a bug report.
as you seem to have found out, items that expired are returned to the character who posted them are can only be picked up from the mail / viewed by that particular character. its possible that you deleted these mails thinking that they were empty before you realised this. in that case the mail will continue to be sent empty until customer service resolves the problem for you....
One of the updates changed it so instead of expired auctions being accessible by any character on your account it is only accessible, (retrieve expired item) from the character that put it on the exchange.