Both Template Designer 2 and Mailing Designer 2 use some behind-the-scenes logic to make sure that your hyperlinks actually go somewhere! The validation checks the hyperlink format and destination (i.e. does the web page exist). Valid URLs meet both criteria.
Valid URLs follow the format below:
<protocol name>://<domain name>.<top level domain name>
For example, http://www.informz.com is a valid URL.
If you enter an invalid URL, Informz displays a corresponding error message.
Pay No Attention to That Man Behind the Curtain...
While hyperlink validation is definitively a behind-the-scenes activity, the underlying concept is pretty simple. Informz first sends a network request to the hyperlink. If it receives a success code (200, 300, etc.), the hyperlink passes validation. If it receives a different response (e.g. a 404 error), the hyperlink does not pass.
Keep in mind that the validation test is not always sure-fire way to determine if the destination address exists and truly works! For example, Informz typically cannot validate hyperlinks to your organization's intranet site because external network requests are usually blocked.
If you need to insert a hyperlink that Informz cannot validate, check the Allow Insert checkbox below the URL. When you click Insert Hyperlink, Informz bypasses the validation and adds the hyperlink to your template or mailing.
As above, hyperlink validation can't always determine if a URL works or does not. Think of it more like a quick reminder to double-check your hyperlink - a "just-in-case" feature that goes the extra step to ensure that your mailings are the best they can be.