Lync is crippled if you're small (O365)
I’m subscriber to O365 for quite some time and Lync wasn’t fully functional (ability to chat with people outside of my domain) for me even once. Solutions I was able to find in Google were all the same, turn off External communications then turn it on again (and it doesn’t work, I’ve tried many times).
Today after some investigation I’ve finally found out where the problem is. It’s wrongly set SRV record.