I'm having the exact same problem ("Generating Mailbox List" forever), with about 300 mailboxes in three accounts. If I look at ~/Library/Application Support/Alfred 2/Workflow Data/com.palobo.mailactions/mbCache.plist , it looks like it has a complete list of mailboxes and accounts. But the "Generating Mailbox List" message doesn't go away, and I can't actually execute any actions.