setacl mailbox for virtual domain ids not working

[Ramprasad]

Hi
I have a cyrus 2.3.7 server running on linux ( centos) with virtual
domains

If I have try to setacls to a virtual domain-id it is not working
>From cyradm this is the error I am getting 

-----------------------------
cyradm  --user=cyrus localhost
IMAP Password:
localhost> sam user/alm1 alm3 at pragatee.com all
setaclmailbox: alm3 at pragatee.com: lrswipkxtea: Invalid identifier

-----------------------

Do I need to escape the '@' in some special way in the id

Thanks
Ram