re :"The current operation on Bulk Mail did not succeed. The mail server for acccount......" What was the rest of the error message ?

Unfortunately, that's all of the message that shows. However, the Bulk Mail has now started opening sometimes, but not consistently.

Bulk mail is unique to yahoo and contains what they consider spam. It may also be quite large for various reasons. When it opens right click the folder select empty Junk to reset it's contents and size. (This will delete the bulk mail in the folder)

Do you have the same issues following the initial emptying of the bulk mail folder.