I needed to setup some DNS records for an Office 365 migration earlier and was initially slightly confused translating the settings Microsoft supplied us to those needed as input on 123-reg’s Advanced DNS configuration. The MX, TXT and CNAME records were simple enough, but it was the SRV records that needed a bit of fiddling to get right.
As an example on the SRV records, MS give you something like this:
| Type | Service | Protocol | Port | Weight | Priority | TTL | Name | Target | |
| SRV | _sip | _tls | 443 | 1 | 100 | 1 Hour | thedomain.co.uk | sipdir.online.lync.com | |
| SRV | _sipfederationtls | _tcp | 5061 | 1 | 100 | 1 Hour | thedomain.co.uk | sipfed.online.lync.com | |
123-reg give you this interface to enter SRV records yourself:
By looking at the examples you can start to understand how to translate the Service, Protocol, and Weight items that MS give you, into the 123-reg input boxes (which do not exist individually for Service, Protocol and Weight).
In the first SRV record example –
Hostname therefore becomes: _sip._tls (the Service + the Protocol with a dot (.) between)
TTL of course becomes: 3600 (1 hr)
Priority is 100
Destination (the most confusing one) becomes: 1 443 sipdir.online.lync.com. (note that it starts with Weight (1), then a space, then the port number (443), then the Target (sipdir.online.lync.com), followed by a dot (.)
That forms your complete SRV record. By entering these along with the other records you require, you should have a fully functional Office 365 setup on your custom domain name.