If you click on the SMTP part of the infographic, it will take you to the settings or you can navigate on the left to those settings. You will need the host and port information (usually the default port is used so you might just need the host) of your SMTP server to be used to send outgoing emails.
Note that having one node is better than a two node cluster. Due to possible issues with "split brain" syndrome, avoid two node clusters. Either use one node and have no failover/load balancing or go with three nodes to get failover/load balancing.