Question on setting up dovecot

[Jeffery Small]

Server OS:   Ubuntu 15.10
Sendmail:    8.14.9-4

# doveconf -n
-----------------------------------------------------------
# 2.2.18: /etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.8 (0c4ae064f307+)
# OS: Linux 4.2.0-27-generic x86_64 Ubuntu 15.10 
disable_plaintext_auth = no
mail_location = mbox:~/lib/Mail:INBOX=/var/mail/%u
passdb {
    driver = pam
}
protocols = imap pop3
ssl_cert = </etc/dovecot/dovecot.pem
ssl_key = </etc/dovecot/private/dovecot.pem
userdb {
    driver = passwd
}
userdb {
    driver = passwd
}
-----------------------------------------------------------

I'm new to dovecot and have a configuration question.  I'm attempting to
have a Windows 7 system on my secure LAN connect to the Ubuntu server
using POP3 on channel 110 and retrieve mail from the /var/mail directory.
The user is defined on the Ubuntu machine and when running the Windows
Internet E-Mail Settings tool, the Test Account Settings Logs onto the
server successfully and sends a test message.  However, when I perform a
Send/Receive operation from the user's Outlook, all steps complete but no
mail is pulled down from the server.

I have tried setting:  mail_location = /var/mail/%u

and restarted dovecot, but nothing changes.  How can I debug this?  I'm
unsure where to look for clues as to what's happening under the hood.  Any
pointers would be appreciated.

Regards,
--
Jeff Small