Do not include the full link

It is important that you do not include the full text of the link. Do not write 'visit http://www.mysite.com' or 'subscribe at https://www.mysite.com/subscribe.html' in your newsletter. This can lead to your newsletter getting flagged as a phishing email.

When sending your newsletter, the actual underlying link is replaced by a link that first leads the visitor past our system. This allows us to measure the clicks. After the measurement, the visitor is immediately redirected to the original link.

The problem here is that in this case the link shown does not match the actual link. This is often seen as a phishing attempt by security software. The recipients of your newsletter may see a warning within their email client. 

Therefore, always change 'visit https://www.mysite.com' into something like 'visit our website', and turn this text into a clickable link by selecting the text and entering the URL.