Я такого опыта не имел. Но говорят что можно настроить.
443 PSOM/TLS
3478 STUN/UDP
5223 UDP
50000-59999 RTP/UDP
I have allowed follow strings at the my proxy.
.outlook.com.
.lync.com.
I wonder when lync uses the proxy and when it bypass!! but all to work
it's need allow that's string in proxy as well as port/fqdn in the
firewall.
Первоисточник: http://www.squid-cache.org/mail-archive/squid-users/201205/0129.html