src/Mail/MimePart.php
public function setContentType(string $contentType, string $charset = null)
    {
        $this->setHeader('Content-Type', $contentType . ($charset ? "; charset=$charset" : ''));

        return $this;
    }
public function setContentType(string $contentType, string $charset = null)
    {
        $this->setHeader('Content-Type', $contentType . ($charset ? "; charset=$charset" : ''));

        return $this;
    }
public function setContentType ( string $ contentType , string $ charset = null ) { $ this -> setHeader ( 'Content-Type' , $ contentType . ( $ charset ? "; charset=$charset" : '' ) ) ; return $ this ; }
Sets Content-Type header.

@return static
Sets Content - Type header .