If you are using the Sametime Gateway and connected to Yahoo make sure you read Technote 1303292. On April 24th Yahoo will be moving to new gateways, so you will need to adjust your firewall rules for the new Hostnames/IP Addresses which are documented in the technote. Thanks for the heads up Vinny.
The technote is in process of being update to include more information regarding configuration changes that are also required. Until the document has been updated, you can see the following post for more details:
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