If you're somewhat unfamiliar with how the web works, and how individuals are tracked and how targeted advertising and web data sales work, maybe the following can help understand a little more about what is likely happening here, and the previous replies... It doesn't matter what organizations you're associated with. Various entities on the internet try to track everybody. Even their own folks get tracked. What web pages you access, what searches you run, who you exchange email with, what you write, etc.
Now as for the complexity of the web... Most of the web pages that we all visit are built from references and from content located across many different web servers, too. While you might go to one web address, the content loaded into and displayed by your web browser can originate on many different web servers, in many different domains, across many countries, owned by different organizations, and each server with many different certificates, cookies and the rest involved. Only the simplest of web pages around these days will load everything only from the web server you are visiting in your web browser.
Now mail itself — specifically HTML-format mail messages — is web content and is very much similar to a web page, and the messages can load what they display from one or more remote web servers. Loading remote image content in an HTML mail format message can cause these errors, as the mail client must access the remote web server(s) involved in the message — these images are commonly used to track who has read a mail message, too — can have certificate problems.
Now.... Getting back to the previous reply I've posted here...
Based on what you're reporting here, whatever web site you're accessing — and HTML-format mail messages can access web sites and web data, particularly if you're allowing mail to load load remote images — is loading data from Casale, or something else running on your computer is attempting to directly access Casale for some reason, and the Casale servers are (again?) having certificate issues. Various apps that look like local apps running on your Mac are really just a form of a web browser, too. Accessing remote data and rendering the HTML for display, for whatever the app was built to do. If it's not Mail or Safari or such directly involved, sometimes figuring out which tool is causing these certificate errors might not be entirely obvious.
There is nothing you can do about this certificate error, so you're left to ignore it. Sooner or later the folks managing the web server involved here will notice and update their certificate. Or you can look into tools or web browser add-ons or alternate web browsers that might offer mechanisms or tools to block web and ad tracking if you're inclined. Or you can potentially block the reference to the failing web server. But that's a more general discussion, and that can sometimes introduce other problems and confusions. If you want to discuss that topic, please consider starting your own discussion thread.