Our SharePoint 2016 farm have 2 WFE, 2 APP, and 2 Search servers.
In the outgoing server settings, we point to our company SMTP (smtp.company.com).
In order to allow the SMTP relay for SharePoint's email, we need to apply firewall open. Although we can simply apply open for all 6 servers but I want to understand the traffic logic.
Should I expect all email will be started from WFE? Or it will be started from other server depends on server role?