delete of @ in emailaddress when starting unsubscribe link in url

You should always encode the url when outputting to a link tag:

urlencode('http://test.domain.nl/[email protected]')

Rewrite

After further examination of your website. It’s clear that the URL is being rewritten when a trailing slash is absent uitschrijven?email=.

Doing research I have stumbled on this issue which is identical to yours.

The solution is to add a RewriteRule rule in your .htaccess file.

RewriteCond %{REQUEST_URI} !(/$|\.)
RewriteRule (.*) %{REQUEST_URI}/ [R=301,L]