Hi Amit,
We haven't tried using TestComplete with Lotus Notes. Also, I'm not very familiar with this product and a quick search on the web does not return any useful information on e-mail clients for Lotus Notes. Could you please give me some more detailed information on the specific name and version of the e-mail client application you use?
BTW, if the non-visual methods do not work properly for you, you can try simply recording the needed GUI actions and sending mails via playing back the corresponding test. This can give you a solution much faster, because if we start investigating the Lotus Notes problem, this can take much time.