Use UTL_SMTP send mail charset thai

Question

when I sent mail by use utl_smtp with thai language.
and I get mail ,I found ????????????? on email
sg := 'From:'||MSG_FROM||utl_tcp.crlf||
'To:'||MSG_TO||utl_tcp.crlf ||
'Subject:'||MSG_SUBJECT|| utl_tcp.crlf||utl_tcp.crlf||MSG_DETAIL;
-- Set Message format
utl_smtp.data(c,'MIME-Version: 1.0' ||CHR(13)|| CHR(10)||'Content-Type: text/html; charset=utf-8' ||CHR(13)||CHR(10) || 'Content-Transfer-Encoding: 8bit'|| CHR(13)||CHR(10) ||msg);
utl_smtp.quit(c);
Help me

Answer 1

msg :=
--'Date:'||TO_CHAR( SYSDATE, 'dd Mon yy hh24:mi:ss')|| utl_tcp.crlf||
'From:'||MSG_FROM||utl_tcp.crlf||
'To:'||MSG_TO||utl_tcp.crlf ||
'Subject:'||MSG_SUBJECT|| utl_tcp.crlf||utl_tcp.crlf||MSG_DETAIL;
-- Set Message format
-- utl_smtp.data(c,'MIME-Version: 1.0' ||CHR(13)|| CHR(10)||'Content-Type: text/html; charset=utf-8' ||CHR(13)||CHR(10) || 'Content-Transfer-Encoding: 8bit'|| CHR(13)||CHR(10) ||msg);
utl_smtp.open_data(c);
-- utl_smtp.write_data(c,'MIME-Version: 1.0' ||CHR(13)|| CHR(10)||'Content-Type: text/html; charset=utf-8' ||CHR(13)||CHR(10) || 'Content-Transfer-Encoding: 8bit'|| CHR(13)||CHR(10) ||msg);
utl_smtp.write_raw_data(c, utl_raw.cast_to_raw('MIME-Version: 1.0' ||CHR(13)|| CHR(10)||'Content-Type: text/html; charset=tis-620' ||CHR(13)||CHR(10) || 'Content-Transfer-Encoding: 8bit'|| CHR(13)||CHR(10) ||msg));
utl_smtp.close_data(c);
utl_smtp.quit(c);