http://xn--fdbk5d8ap9b8a8d.xn--deba0ad/ is the actual target.
I see a dot between the 8d and the xn--, and my Firefox even
renders it with a '.' (see attached .png).
Same here with IE6 on a box where I've not yet installed FF. But
the zone cut is the TLD:
`nslookup -q=ns xn--fdbk5d8ap9b8a8d.xn--deba0ad`
| primary name server = [...]
RFC 2142 says "only the organization's top level domain name are
required to be valid." For your example that would be xn--deba0ad,
resulting in a likely unusable abuse(_at_)xn--deba0ad address.