Reverse DNS Lookup
This tool will provide you the hostname (ie www.yahoo.com) of the IP address that you enter below.
Results:
Lookup on IPv4 Address: 134.91.50.10
Hostname: webmailer.uni-due.de
Hostname: webmailer.uni-duisburg-essen.de
Hostname: webmail.uni-due.de
Hostname: webmail.uni-duisburg-essen.de