I am posting this in case anyone else is experiencing a similar problem. This morning I have started seeing the dreaded password dialogue box in Outlook when attempting to access my primary IMAP account on BT Yahoo. I do not have a problem accessing a secondary IMAP account which has been transferred to BT Mail, nor do I have a problem accessing my BT Yahoo mail via POP or via the web. In other words, this seems a problem exclusive to my BT Yahoo IMAP account. This is not exactly the end of the world and I have simply switched my POP account for the IMAP account in my send/receive group in Outlook (which for non-Outlook users means I have disabled automatic mail checking for the IMAP account).
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