If anyone here uses yahoo mail via an imap connection and you've been wondering why it's slow, they've reduced the number of simultaneous imap connections your client can create to their imap server.
Imap is a slow mail protocol - it takes a long time to download a list of emails on the server. Outlook (and probably others) get around this by opening up multiple connections to the server to grab mail headers in smaller batches - multiple connections mean that the email headers are downloaded quicker.
I've been working on my imap mail exporter this week (untouched for a couple of years) and noticed that the maximum number of connections the program is able to establish is just 4. With GMail i can hit 12 connections and that's a limit i imposed due to GUI refreshing woes.
Yahoo has always been iffy. Now it's confirmed. Insecure passwords, passwords kept in text files, multiple hacks and now after Marissa Mayer did her worst to destroy the service entire (why???) they're now limiting the amount of connections you have.
Needless to say i'm downloading as much as possible..
I need a new signature... i'm bored of the old one!