[Dovecot] Dovecot and /dev/shm

[DJ GRP]

Hi,
I have tried to use /dev/shm for Dovecot's index files:

> mail_location = mbox:~/mail:INBOX=/var/mail/%u:INDEX=/dev/shm/%u

But it does not seem to like it.

May 21 07:13:59 IMAP(user): Error: stat(/dev/shm/user/.imap/INBOX) 
failed: Permission denied (euid=1234(user) egid=500(group) missing +x 
perm: /dev/shm)

It seems to me that /dev/shm permissions are OK. Any suggestions on how 
to achieve this?