If you wish to use your WordPress site as your main site you will most likely use it on mydomain.com and www.mydomain.com
In such a scenario the steps would remain similar as above, but you will need to point an A record for you root domain (mydomain.com) to 34.149.157.183 and a CNAME for your subdomain (www.mydomain.com) to wp.msgsndr.com. An example of such a setup is given below.
A record for mydomain.com
CNAME for www.mydomain.com
