EmailEncoding in Users table

In RT 3.0.9, there is an EmailEncoding field for all users in the users
table, always set to the default NULL. What is this field used for? Is it
set automatically? Does it appear in the UI anywhere?

For Japanese and Chinese language users, I need to encode output differently
for various web-based e-mail domains (e.g. www.yahoo.co.jp). In anycase,
utf8 is a non-starter across the board.

Thx,

Ed