no btinternet mail download after upgrade to maverick
Here is the best resource when troubleshooting issues with email.
OS X Mail: Troubleshooting sending and receiving email messages
I use BTInyternet and have had no problems.
Are you using mail.btinternet.com for both SMTP & POP? If your using Yahoo servers then you will need to change as BT are no longer using Yahoo for email and are in the process of moving all email to other servers.
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