[Dovecot] E-mail not being processed into Dovecot folders

[stalker]

I have a new CentOS 6 server running Dovecot 2.0.9
It has current patches from CentOS.

Pasted below are the version and output from dovecot -n
When I run mail -s "test" username
test
<ctrl-D>
mail is written to /var/spool/mail/username
and not to /home/username/Maildir/

The user's client software, Thunderbird, logs in but since mail
is not written to Maildir it thinks there is nothing (see paste below 
from /var/log/maillog)

How do I get sendmail or what ever MTA processes mail to write to 
Maildir rather than /var/spool/sendmail?

[root at info2 Maildir]# dovecot --version
2.0.9
[root at info2 Maildir]# dovecot -n
# 2.0.9: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-279.19.1.el6.i686 i686 CentOS release 6.3 (Final)
disable_plaintext_auth = no
mail_debug = yes
mail_location = maildir:~/Maildir
mbox_write_locks = fcntl
passdb {
   driver = pam
}
protocols = pop3
ssl = no
ssl_cert = </etc/pki/dovecot/certs/dovecot.pem
ssl_key = </etc/pki/dovecot/private/dovecot.pem
userdb {
   driver = passwd
}
protocol pop3 {
   pop3_uidl_format = %v.%u
}


Jan 10 08:11:13 info2 dovecot: pop3-login: Login: user=<username>, 
method=PLAIN, rip=192.168.55.50, lip=192.168.55.8, mpid=30560
Jan 10 08:11:13 info2 dovecot: pop3(username): Debug: Effective uid=503, 
gid=503, home=/home/username
Jan 10 08:11:13 info2 dovecot: pop3(username): Debug: maildir++: 
root=/home/username/Maildir, index=, control=, inbox=/home/username/Maildir
Jan 10 08:11:13 info2 dovecot: pop3(username): Disconnected: Logged out 
top=0/0, retr=0/0, del=0/0, size=0