Sometimes orgs have trouble with email deliverability due to various settings. An example of this is Simpplr emails getting sent to spam folders, or being shown as potentially hazardous in your inbox. Setting up a DKIM (DomainKeys Identified Mail) key is often a solution for these issues.
This Salesforce article will walk you through the steps needed to create a DKIM key for your org's email settings.
Before setting up a DKIM key, be sure to work with your IT Security team to make sure this is applicable to your company. The article also contains key considerations before setting this up.