Why are the letters heading in the letter krakozyabry?

Question

Yii

I use yii2 and the swiftmailer built into it I
send an email. The text comes in fine, but the header "=?utf-8?Q?=D0=9E=D1=82=D0=B2=D0=B5=D1=82_=D0=BD=D0=B0?==?utf-8 ?Q?_=D0=B2=D0=BE=D0=BF=D1=80=D0=BE=D1=81?="
What is this nonsense? The encoding is utf-8 everywhere.

Answer 1

Keyword "Quoted-Printable". It's Unicode, but you need to work with it.