Figure 1
Figure 2
This is the publicly addressable URL for your Sitecore instance. Note that this may only be open to Salesforce IP addresses via firewall pinhole, and it may also be an IP address.
Figure 3 - Salesforce: Adding Sitecore Email Campaign Messages to the Contact Layout
Figure 4 - Salesforce: Adding Get Sitecore Email Campaign Analytics button to the Contact Layout
Contact Layout with the Sitecore Email Campaign Messages related list and the related button:
Next Step
S4S EXM with CD/CM Servers (Pre-Sitecore 9)