Make sure that you do not display URLs in plain text that are being tracked.
As soon as a recipient clicks on a link that is to be tracked, the browser first opens - for a tiny moment - a web page on a server of your email marketing provider (in this case Quentn). The click is registered there and the recipient is immediately redirected to the actual target page. This process allows you to see afterwards how many recipients (and possibly which recipients) have clicked on the link.
BUT: If a link is displayed in plain text in the email, there is no match between the URL that is displayed to the recipient and the URL to which they are initially directed. Many email providers and clients interpret this as a phishing or fraud attempt and either move the email directly to the spam folder or at least display a very clear notice. Both have a negative effect on the sender's reputation and should therefore be avoided.