[EXIM] I can't get exim to deliver mail to local users!

I have installed exim v1.82 on redhat linux.

The hostname is mail
The domain is cis.co.uk

I have defined users using the control panel and mail files have been
created for these users in /var/spool/mail.
I have set the sticky bit for /var/spool/mail.
I have amended the local_delivery transport in the exim configuration file
as follows:
local_delivery:
        driver=appendfile
        file=/var/spool/mail/${local_part}

By executing 'exim -bP' I can verify that local_domains = mail.cis.co.uk
By executing' exim -brw username' I can verify that all the addresses would
be set to username@???
By executing 'exim -v -bt username' I get the following:
username@???
        local delivery to username in domain mail.cis.co.uk
        director = localuser, transport = local_delivery

Why is it that when I send a mail message to username@??? it just
sits in the exim input spool directory and doesn't get delivered to the
user's mail file in /var/spool/mail?

I've never set up a mail server before and know that I've probably forgotten
something really basic but for the life of me I can't see what it is.

Could someone please advise me?



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