How can a ASA firewall or router be configured to block small company's employees from accessing their Yahoo email and chat services?
Very simply put, block the IP range.
deny ip (your network) (your mask) 188.8.131.52 0.0.63.255
That will block all communications to all of Yahoo's IPs (at least in the US) if used in an extended access list. I believe it even encompasses the IM servers.
you need to create a access-lists to resolve your issue.here's is the sample configuration.go thru the following link
Thanks and regards
+91 98940 44411,firstname.lastname@example.org