UTF-8 error in UE4

I might be wrong, but it seems, DA still has not made its homework for full UTF-8 compatibility with all of its products. :-(

I created a simple form which I want to deliever to 2 recipients. It is a client's feedback form to order a free diabetic device.
The header of the modified block template shows:
FEEDBACKFORMULAR von diabetes-austria.com
OneTouch® UltraEasy® oder OneTouch® Vita® kostenlos anfordern
but should be:
OneTouch® UltraEasy® oder OneTouch® Vita® kostenlos anfordern
Each Umlaut is turned into some double-byte "monster":

Ãœbermittelt instead of Übermittelt

Every file was put to UTF-8, but the incoming mail's source code shows:

MIME-Version: 1.0
Content-Type: multipart/alternative; charset="ISO-8859-1"; boundary="WAMULTIBREAKWA"

and further down:

--WAMULTIBREAKWA
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: quoted-printable

Where are these hidden wrong "ISO-8859-1" created????

Also, the file called "waue_FILEFORMNAME.php"
holds this part of code (from line 1):

<?php
$MailAttachments = "";
$MailBCC = "";
$MailCC = "";
$MailTo = "";
$MailBodyFormat = "";
$MailBody = "";
$MailImportance = "";
$MailFrom = "".((isset($_POST["Email"]))?$_POST["Email"]:"") ."";
$MailSubject = "my subject";
$_SERVER["QUERY_STRING"] = "";

//Global Variables

$WA_MailObject = WAUE_Definition("","","","","","ISO-8859-1");

if ($RecipientEmail) {
$WA_MailObject = WAUE_AddRecipient($WA_MailObject,$RecipientEmail);
}
else {
//To Entries
.....


did I simply over - read a set-up issue?

please, point me to the right direction.