Lately, I received several complaints from customers about the use of links in emails. In order to be able to track the click behavior of the recipient, the system automatically replaces the link by a redirect link. This is described in the following docs article: https://docs.microsoft.com/en-us/dynamics365/marketing/email-design#add-standard-required-and-specialized-links-to-your-message
Once the recipient opens the email in the inbox and hovers over the link with his mouse, the redirect link is displayed. This is a URL with random characters, like this example:
https://6d9fdf51da054e62bd4743a6btcf2aaf3.svc.dynamics.com/t/t/FdbVlxti4aMSIBZDFdknBCc5A4wESmXdxEAXfJoLLRQx/VC4FfIW1IivoK5vfUKZ0zevxOho8cIGpjMQeqjpvjcj8x

This looks insecure and unreliable and recipients are less likely to click on the link because they don't trust it.
Other marketing tools allow to add a prefix in front of the url, for example the sender domain. The redirect link would look like this then:
https://.6d9fdf51da054e62bd4743a6btcf2aaf3.svc.dynamics.com/t/t/FdbVlxti4aMSIBZDFdknBCc5A4wESmXdxEAXfJoLLRQx/VC4FfIW1IivoK5vfUKZ0zevxOho8cIGpjMQeqjpvjcj8x