mime email base64 headers vs. utf8: first break into lines, then encode?

Question

Let\'s take this Subject line,

$ echo -n 台電用戶意見電子信箱-信件受 | base64
5Y+w6Zu755So5oi25oSP6KaL6Zu75a2Q5L+h566xLeS/oeS7tuWPlw==

Some mailers (A cer