Hi  Vakantiehuizen,

If you're referring to an inbound link or page being indexed containing query string parameters e.g. example.com?utm_source=x, then yes...these may cause issues with duplicate content and SEO. If you have pages with these parameters on your site then you should use the rel="canonical" tag to specify the canonical URL that you'd like Google to rank. Also, you should never include these parameters for internal links on your site.

Although I don't know what you mean when you say "UTM tag link is not a natural link". Could you explain?

I don't think you need to be overly concerned about this if you're already using rel="canonical".

We regularly receive inbound links with these parameters included in them.

The reason why this happens is that we included these parameters to track some of our email and social campaigns and sometimes people find these links and link to them. These are perfectly natural, just that the people that link to them might not know about these parameters and may think they are part of the URL and the links may not work without them.