Use curl to send a static xml file using url encoding to a web page using pos

Hi I am try to use curl to send a static xml file using url encoding to a web page using post. This has to go through a particular port on our firewall as well. This is my first exposure to curl and am not having much success, so any help you can supply, or point me in the right direction would be greatly appreciated.
I also have a quick question concerning post; does the post command record the originating address? The reason I am asking is that the web page I am sending the xml to requires that the connection be made over the internet from one machine's ip to the other machine's ip over an open port on our firewall. We are configured with an open port on the fire wall but for security reasons the ip address is on firewall as well, this is were traffic is being directed to and from both machines.
When I send the post command from the the originating machine would the web page that receives this become confused, as it is not coming from the ip address it is expecting?
thank you for your time.

Deivering a file using POST is usually mime encoded, but I guess anything is possible, as long as the receiving web server and service like the message. Getting curl to post a file at all is the first question. Browsers do (in mime), so curl might well do this, too. The file can just be a really big string form variable. Google finds this right off: bash - Unix cURL POST to specific variable using contents from a file - Stack Overflow

xml can and often has urlencoding in some places, but you can reencode the whiole file using urlencoding to make it palatable to web delivery.