internal/coding/idheader.go
func ToIDHeader(v string) string {
	v = url.QueryEscape(v)
	return "<" + strings.Replace(v, "%40", "@", -1) + ">"
}
func ToIDHeader(v string) string {
	v = url.QueryEscape(v)
	return "<" + strings.Replace(v, "%40", "@", -1) + ">"
}
// ToIDHeader encodes a Content-ID or Message-ID header value (RFC 2392) from a utf-8 string.