Thank you for reaching out to the Community with your feedback on our event links. I can definitely understand how important it is to shorten these links. I took a peek at your account and can see links in your emails don't have special characters that would affect your email from being delivered properly. Because of this I would suggest whitelisting Constant Contact.
Are your test previews going into your spam/junk folder? Also, what is the name of one of your campaigns you're experiencing this with? Once we have these details we can troubleshoot this further for you. Feel free to also reach out to our Deliverability Specialists. These support agents can help look further into this email campaign or any other campaign that may not be delivering to your inbox.
2 Years later and I had to google how to fix this... still no warnings or email... nothing to let me know what is the problem... Why does Constant Contact not let us know?