I moved the topic =)
I have no xajax for YOM, but mails, so I can assume you mean that.
Yes, the JS is loaded, of course. All you need to do is to register your function.
revise the (poorly named and soon to be renamed) mailinfo_*.php
$xajax->registerFunction("mail_status");
is done in the common, however, I require that thing only in the page_footer() as far as I now.
I supposed you would EDIT the files directly

to register your function if necessary.
the mailinfo_server.php contains then the function that is called. (an example is the mail_status).
If you have (my mental capacities are quite taken at the moment) a good outline to make it work better (I am an Ajax n00b), they are welcome =)
My plans for the AJAX commentary are currently on hold... due to the links contained within and hence rewriting with the response the allowednavs ... which I see as a security loophole of some size and bad patching and fixing to be done Oo