Recently had some problems with email on my phone. For some reason, the emails would not send. Today, I was able to mysteriously fix the problem by deleting all the outbox items that had been queuing to be sent and when I sent another email, it went off without a problem. This was a surprisingly easy fix for a problem that had me looking into every section of the phone's settings, connectivity, email, internet and preferences over and over again. If you have a mysterious problem sending emails from your N8, maybe try delete all the emails from your outbox and try again.
Another thing I discovered was that the Nokia email program does not allow you to send any attachments that exceed 4mb. This bombed my idea of uploading videos and photos via facebook's upload-by-email function. Anyway I am sure you all would find it useful to know the size limit for attachments.