We have discovered some problems with the reverse DNS delegation.
From our investigation it looks like the problem is in RIPE (http://www.ripe.net) database.
RIPE has been notified about that issue and they are investigating it now.
This may affect email delivery.
Sorry for all inconveniences caused.
Swift Internet NOC 
Response from RIPE:
Between 15:00 UTC and 18:00 UTC on 13 June 2012, there was breakage in reverse DNS services. Queries may have resulted in empty results. The problems have been fixed and should propagate out in the coming hours.
source:
http://www.ripe.net/internet-coordination/news/announcements/reverse-dns-services-issues
However for us this service is still not working properly.
We have got a confirmation from RIPE that the issue has been definitely resolved. Our reverse DNS delegations respond fine now.
Update from RIPE:
Currently the vast majority of reverse zones has been restored. For a limited number of zones restoring the zone will take longer than expected, therefore these zones may still return empty responses.
The zones known still to be affected are listed below:
0.4.1.0.0.2.ip6.arpa
185.in-addr.arpa
4.1.1.0.0.2.ip6.arpa
5.1.0.0.2.ip6.arpa
6.1.1.0.0.2.ip6.arpa
7.0.1.0.0.2.ip6.arpa
7.1.1.0.0.2.ip6.arpa
7.4.1.0.0.2.ip6.arpa
8.0.1.0.0.2.ip6.arpa
a.0.1.0.0.2.ip6.arpa
a.1.1.0.0.2.ip6.arpa
a.4.1.0.0.2.ip6.arpa
b.0.1.0.0.2.ip6.arpa
b.1.1.0.0.2.ip6.arpa
b.4.1.0.0.2.ip6.arpa
source:
http://www.ripe.net/internet-coordination/news/announcements/update-regarding-the-reverse-dns-services-issues