[Exim] permission problem: stumped

Hi List.

I have created a local account on my gateway to which I send the untagged
spam & false positives to in order
to train SA.

I have checked the permissions.
EXIM runs as xadmin.

I have changed the group of spam & nonspam to that of xadmin. I am in still
getting the error below:

2003-10-29 07:35:16 1AEWHt-0006qZ-Kt == spam@??? R=localuser
T=local_delivery defer (13): Permission denied: creating lock file hitching
post /var/mail/spam.lock.jp-mx-1.mtnns.net.3f9f89d4.000005a9 (euid=516
egid=510)

any help would be appreciated.

Thanks

Regards,
Tom Kinghorn