Listening on ipv6 only?

[Beonix]

Running Zimbra 7.1.0 on ubuntu 8.04 x64
Running SSL IMAP on 993, SSL SMTP on 465.

When doing netstat -tulpn|grep 993 I'm getting:

tcp6 0 0 :::993 :::* LISTEN 7455/java

Does this mean that Zimbra listens on ip6 993 only? How can it be? Intended or a bug?

I don't even have IPv6 address assigned to any interface.

[olivierfaber]

I am having a similar issue with Ubuntu 10.04 & an upgrade from 7.0.1 to 7.1.1.
After the upgrade, zimba only listens on IPv6:

sudo netstat -anltp | grep :443
tcp6       0      0 :::443                  :::*                    LISTEN      5571/java

There is one difference, my VPS does have an IPv6 address. That address is not actively in use but I would like to have it enabled for future use..

Is there a way in which I can enable IPv4 and IPv6?