You have the UE behavior set to redirect to the aanmeldentks.php after sending the email, does this redirect occur?
No, it doesn't
I run my own server. It's supposed to use sendmail
$MailBody = $MailBody . (GetFromPage("../../aanmelden_WAUE_HTML_WA_Universal_Email_1.php"));
this is a temp file created by UE, and should not be used for the email template.
you should select to use one of the em,ail templates and not chose the UE temp file.
Changed it to Default