Link in E-Mail notification changes (for tracking reasons?)

Hi! 

I have a donation button on my website. Everyone donating gets a downloadlink for my shopping guide in the e-mail donation reciept. When I click the link in thunderbird it gives me a warning that the linktext does not match the link. However when editing the donation receipt I see that the link matches exactly the link text. Since clicking the link brings me to the actual content, I assume there is some analytics/tracking added to this link. I don't wont that. Can I change it? (only workaround would be to to change the link text to something else but I like if the user can copy & paste the link text as well.

This is the error thunderbird gives me: 

This is the link I put into the mail: 

I blacked-out the exact link because I do not want it to be on the internet. But as I said link and text is the same. But when reciecing the email the link is different....

I just realised that because of this rightlick - save as does not work as well. So this is a real problem for what I want to do. 

sorry for my late reply. Your suggested solution is what I use now. Thanks for answering