Setting up DNS SRV records for an Office 365 migration (on 123-reg)

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
SRV _sipfederationtls _tcp 5061 1 100 1 Hour

123-reg give you this interface to enter SRV records yourself:

Screen Shot 2013-06-13 at 14.24.42


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 (note that it starts with Weight (1), then a space, then the port number (443), then the Target (, 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.


  1. Sean – I’ve had issues with lync when it comes to invites (couldnt accept my own invite from an email but could from the desktop app!).

    Having made the change to “_sip._tls” and “_sipfederationtls._tcp” as well as 3600 (rather than 1) its all working perfectly.

    Been bugging me for a while so I’m very grateful for your clear explanation 🙂

  2. Sean – very useful.. and simplifies the task. thanks for that. Just one correction in your write up above:
    You say ‘Priority of course becomes: 3600 (1 hr)’ — this should be:
    TTL of course becomes: 3600 (1 hr)
    Priority is 100

  3. Great stuff.. just the info I needed. I was almost there, but didn’t get where the protocol should have been entered. Many thanks.

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