I think if you install Kumudam Tamil Font [freely available in Kumudam.com] you can read all the tamil mails easily. For Tamil, I think all PCs will be havingEltpan-n fonts i.e. ELANGO-TML-Panchali-Normal [TrueType] and WebTamil Normal [True Type]. Try to install the above if not installed. Our group experts may guide you more on this.
With regards,
veegopalji
Edit by Moderators
This is not because of Tamil Font Issue. It depends upon your browser setting, if you selected UTF-8, it will work. If you use yahoo group to post/respond messages unless you change your encoding setting to utf-8, the characters will be unreadable.