You have tried to add a link in your campaign that leads to a website. You type the domain, but when you click Use, you see a red notification telling you that the link won't work on email send. This is because the domain that you are linking to is a bit more strict on the rules of how they would prefer to be visited. Let's get into some details. The following explanation does get a little technical:
The HSTS issue
If you are using your own domain instead of our Loopify domain (firstname.lastname@example.org) and your links form your email don't seem to work properly, there is a high chance that your domain has a strict policy on links:
Strict-Transport-Securityresponse header (often abbreviated as HSTS) allows a web site to tell browsers that it should only be accessed using HTTPS, instead of using HTTP."
Now, what does this mean?
We are using MailGun as an email provider to send emails and they do not support forced HTTPS redirects. If there is a strict domain that forces HTTPS redirects via HSTS, the tracking link cannot finish the callback to MailGun's servers and it results in a failed link. Here is a MailGun article on HTTPS tracking and how to set it up.
MailGun currently doesn't have any workarounds when HSTS is used with their tracking features. If the tracking cookie (after the /c/ in the URL) wasn’t generated by the domain in the URL, the link will not resolve. Unfortunately, MailGun cannot allow a redirect to occur, and it is important for them not to do this because of phishing campaigns and the possibility to derail someone.
The HSTS can also include sub-domains if any request made to your site could have the following Response Headers property: Strict-Transport-Security: max-age=16070400; includeSubDomains.
So, if you are using HSTS on your domain, an option would be to disable it, use a different domain with HSTS disabled, or you can always use our own sender domain that goes through lpy.io instead.