I don't know if this great WP plugin is still maintained.
I found a little bug that can easily be corrected. This is related to the fact that the phpmailer class does not handle the charset encoding the way the author intended it to. Even if you set appropriate headers, they are stripped and replaced with the default iso-8859-1 encoding (wp-include/class-phpmailer.php line 50).
You should thus add this line to your plugin when initializing the phpmailer class:
$phpmailer->CharSet = get_option('blog_charset');
This corrects all issues with accentuated / non-ascii characters.