Clicking on a (tracked or untracked) link with UTM parameters in a Marketo Email resolve with the UTM parameters stripped out.
By default, it's possible to have UTM parameters within links in Marketo emails without issue.
If the UTM parameters are being stripped out, there's likely a 302 redirect occurring whose settings do not allow the passing of these parameters. These settings are on the receiving end and cannot be changed by Marketo. If this is happening internally, you may need to work with your IT department to resolve it.