Set a cookie if the URL contains specific UTM parameters.

setUTMCookie.js

function setUTMCookie() {

    // Search the URL
    var url = window.location.search;

    // Store the UTMs we're searching for in a variable
    var emailCampaignUTMs = '?utm_source=digg&utm_medium=email&utm_campaign=free_plus_shipping&utm_content=hhc_bundle';

    // Calculate the expiration date for our cookie (1 year from the date it's set)
    var cookieDate = new Date;
    cookieDate.setFullYear(cookieDate.getFullYear() + 1);

    // If the URL contains the UTMs we're searching for, set a custom cookie named 'omCustomCookie' and store the UTM string as the cookie value, and expire it one year from the date it is set
    if (url.indexOf(emailCampaignUTMs) !== -1)
        document.cookie = 'omCustomCookie=' + emailCampaignUTMs + '; expires=' + cookieDate.toGMTString() + ';';
}

// Run our cookie function
setUTMCookie();