A guide to generating UUIDs with SalesForce
%%user_crm_id%% pulls in the prospect's Lead or Contact CRM ID
%%subject%% pulls in the email subject line
By combining these tags we can successfully create a dynamic UUID and our key parameter would therefore look something like this:
Custom variable tags can also be created and added to the default variable tags above to ensure each key value is unique.
NOTE: the same UUID must always be passed into the key parameter of both the anchor and image tag