[exim] Mail getting deleted??

Hi,

I've received an email today according to the logs (I've xxx ed out
sensitive data):

2009-03-12 17:26:34 [23137] 1LhcUk-00061B-7k <= L.H@??? H=xxx
(mail.xxx.com) [x.x.x.x]:xxx I=[x.x.x.x]:25 P=esmtps
X=TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32 CV=no DN="" S=520859
id=H000006a00052400.1236832054.mail.xxx.com@MHS T="xxx xxx xxx" from <L.H@???
> for user@???
2009-03-12 17:26:34 [23173] 1LhcUk-00061B-7k => user <user@???
> F=<L.H@???> P=<L.H@???> R=virtual_local_mailbox
T=virtual_local_md_delivery S=520859 QT=24s DT=0s

However, when I grep the mail dir for any reference to this id
"H000006a00052400.1236832054.mail.xxx.com@MHS" I can't find anything.
Does this seem a bit odd, provided that the "user" has not deleted the
email from their email client?

virtual_local_md_delivery is using driver = appendfile to a local
maildir which is locally mounted: /dev/sda2 on / type ext3
(rw,noatime,nodiratime,errors=remount-ro)

There are a couple of other emails which apparently have gone missing.
Thanks for any input.

Kind regards
Samuel