This question really depends on if you are running Skype for Business on premise, or running it through Microsofts online application. They both require different ports, but I don't believe Skype for Business online uses port 5061 so you are probably using an on-premise server, but you should verify with whoever is running your Skype integration. IF this is Skype for Business on premise then the ports that they are using are listed HERE. Be aware that just because Skype for Business on prem is setup to use a specific port by default, your system admin could have set it up to use any port that they please. Therefore, I would double check that the ports listed were the ports used at the time of install. *Port 5061 specifically is used on front-end servers for internal SIP traffic, and SIP communication from the Front End servers to the Mediation and Monitoring servers. THIS link will guide you through everything that Microsoft states needs to be open for Skype for Business if it's being ran through their online service, note that port 5061 is not mentioned here.
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