The March 2017 Marketing Cloud release (which occurred on 4/7/17) included numerous updates across the application, including a new Send Management settings page for URL Expiration! Up until this release you were forced into the default settings, but now there are some new options available.
The URL expiration comes into play a certain amount of time (in days) after an email has been sent. Once this time limit has been reached, the links in your emails will no longer direct your subscribers to the URL behind those links. Your subscribers will instead be redirected to a page to inform them that the link has expired. Prior to this release, the time was automatically set to X days and subscribers were redirected to a system default URL that pointed to a generic expired link page.
We’re excited to see that there are now custom options available for URL Redirects (found under Email Studio > Admin > Send Management > URL Expiration). You are now able to set the time to anywhere from 60 to 730 days (2 years). While it is rare for an email to be clicked 60 days after it is received, it is nice to be able to determine the time frame that fits your specific case. In addition to setting the time, you can now also override the default redirect page to a URL of your choosing. This provides an opportunity to direct subscribers to a landing page on your company website, rather than losing their engagement altogether.
For more information about Salesforce Marketing Cloud URL Expiration, visit the documentation page on the topic at: https://help.marketingcloud.com/en/documentation/exacttarget/admin/url_expiration/