How to post data with REST service from remote server - rest

Question

I am new to REST so bear with me if I'm missing something obvious.
Any pointer would be much appreciated as I am a bit lost.
Scenario
I needed to post some data to the following REST service: https://api.dotmailer.com/ from my web application https://myapp.com/.
During testing, I was able to post the data from my local pc.
However, as soon as I published the updated application to https://myapp.com/ on a remote server, I was no longer able to post any data.
What I've tried so far
Added rule to the remote server firewall to allow outgoing traffic to use https. Didn't solve the problem.
Disabled the url rewriting rule that change http to https for myapp.com. Didn't solve the problem.
Pasted the URL I use to post my data (https://api.dotmailer.com/v2/address-books/12345/contacts) in a browser on the remote server, entered the correct credentials, but couldn't access it.
the error message said "Unable to open this internet site. The requested site is either unavailable or cannot be found." If I do the same on my local PC I can access the URL.
Monitored the two calls with Fiddler2.
I include the results of the monitoring process below:
CALLS MADE FROM REMOTE SERVER
----------
POST /bla.aspx HTTP/1.1
Host: myapp.com
Connection: keep-alive
Content-Length: 10660
Cache-Control: max-age=0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Origin: https://myapp.com
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36
Content-Type: application/x-www-form-urlencoded
DNT: 1
Referer: https://myapp.com/bla.aspx
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8,it;q=0.6
Cookie: ASP.NET_SessionId=xxx; Myapp=xxx; GUID=xxx
CALLS MADE FROM LOCAL PC
----------
POST /bla.aspx HTTP/1.1
Host: localhost:xxx
Connection: keep-alive
Content-Length: 10656
Cache-Control: max-age=0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Origin: http://localhost:60675
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36
Content-Type: application/x-www-form-urlencoded
DNT: 1
Referer: http://localhost:xxx/bla.aspx
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8,it;q=0.6
Cookie: __eqtUser=xxx; ASP.NET_SessionId=xxx; Myapp=xxx; GUID=xxx
Question
I believe point 3 shows that the cause is some setting on the remote server.
Does anyone know what it could be? Or am I completely off-track?
Update
I spoke with the developer on the receiving end of my calls who can monitor incoming traffic.
He could see my local calls but not the ones submitted from https://myapp.com.
In response to gmlime reply, I've added the following to myapp.com web.config file but didn't help.
<system.webServer>
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*" />
</customHeaders>
</httpProtocol>
</system.webServer>
Should I put it at a higher level in the hierarchy?

Answer 1

Make sure that this gets added to the response:
YourAddHeaderMethod("Access-Control-Allow-Origin", "*");
Many servers deny posting from other domains and can terminate the connection. You can learn more about it from the w3 docs for Access-Conrol-Allow-Origin and Mozzilla covers some scenarios. You may have to check with the server administrator to rule out cross domain problems also.