Migrated all of my email identities from older Windows 10 computer (Toshiba Satellite) to newer and faster computer (iMac with Bootcamp set to boot Windows 10). I had problem before with download speed (had to click Get Messages and wait through very long display of "Checking Inbox for new messages" several times, with the message disappearing without downloading any messages (which my iPhone, using native iOS Mail, had already received an hour or two ago), then downloading began, eventually ending with "xxx messages downloaded," but still behind the iPhone's inbox. The idea of migrating was to make it work faster, but this new computer seems to be even slower. In addition, when I click Get Messages "too soon," whatever that means, I get an error message titled "Error with account xxxx," with the text "The account xxxx is being processed. Please wait until processing is complete to get messages." But there is never any alert to tell me when the "processing" completes; I just have to wait a while and keep trying. I do have a very large inbox, and also a number of messages (but there is no way to count them) open in tabs. I need to prune both, but I need decent response in order to do that (and I have to keep up with new messages at the same time). Any idea what I can do to get rid of this message and speed things up? (My email is in att.net, meaning it is managed by Yahoo! The iPhone, naturally, uses the IMAP server, while Thunderbird on Windows uses POP3.)