Adding a domain to Office 365 requires adding some DNS records.
The details are explained here Create DNS records at any DNS hosting provider for Office 365.
But, there are no clearly instruction to add
SRV record with PowerAdmin.
Below you can find our setup for a
Name: _sip._tls Type: SRV Content: 1 443 sipdir.online.lync.com Priority: 100 TTL: 3600
Name: _sipfederationtls._tcp Type: SRV Content: 1 5061 sipfed.online.lync.com Priority: 100 TTL: 3600