Why? Wrong configuration or the email servers are not pop3/smtp?

Only if your email use pop3/smtp in my opinion. Or you will need a plugin.
Can you use MS Outlook (not the Express) to get/send mail?

Can you see in the headers of the messages (Right click the message, choose Properties and Details), for instance:

X-Antivirus: avast! (VPS 0XXX-X, XX/XX/2004), Inbound message
X-Antivirus-Status: Clean