Hello Mohan,
oacs 3.2.5 supported the option to send Emails in html... I can remember that I had to fix some bugs on the spam module to make html-emails work, but now it works. You could see how it worked in 3.2.5 and port it to 4.x
Also check out this thread:
https://openacs.org/bboard/q-and-a-fetch-msg.tcl?msg_id=0001oG
