thank a lot for your feedback,
I tried to go for 'render_page' hook, and it seems fit my case, only one more question..
I've seen, debugging code, that the html that I'm trying to fetch, is inside $this->rcmail->plugins->output['TEMPL....'] or something similar.
If I try to get this key, perhaps, rcmail return me an error. How can I retrive TEMPLOBJECT value?
Thanks in advance for your patience.