When you link to a website from an Infusionsoft email, Infusionsoft will (by default) add an inf_contact_key parameter to the end of the URL. This parameter is unique for each contact, and can only be used by official Infusionsoft pages (such as order forms and web forms). There is no benefit of having it added to non-Infusionsoft URLs, such as links to your company’s website.
Worse, it makes every URL a unique URL. This can prevent your caching from working properly. Instead of loading a cached page, your web or proxy server will have to load the page from scratch. This makes your site load slower and hurts the overall experience for your users. Fortunately Infusionsoft provides an option to keep this from happening.
In your Infusionsoft app, go to Marketing→Settings then click on Email Defaults. Scroll down and select Yes for “Only append inf_contact_key to links going to White Listed Domains?”. Make sure infusionsoft.com is listed in the White Listed Domains box. Don’t forget to hit Save!
Once this option is set, Infusionsoft will only add the inf_contact_key parameter to links going to infusionsoft.com pages, such as your order forms and shopping carts.