ah, ok. In that case you should start with the CGI docs here. As you can see, you print the header like this:

use CGI;
my $q = CGI->new;
print $q->header();
### generate and print more stuff for the web page here
[download]

As suggested previously, you can use LWP::Simple to send your stuff and capture the response from the remote server, which might tell you if the message has been sent successfully if that service is well implemented. If you do get a "receipt" then it will probably be in XML format and you will then want to use a module that helps you with parsing the XML, something like XML::Simple (there are many options).