I'd like to recall a blogpost that we published in 2016 about how to enable tenant specific SMTP support in WSO2 Identity Server:
Since moving to WSO2IS v5.3.0 onwards a lot of things changed. Using the Axis2 layer to configure email support became a legacy solution. Meaning that there is no guarantee that the email plugin we've published in 2016 will work now. Using the CEP engine integrated with Identity Server is the primary approach chosen by WSO2.
This blogpost will present a new solution for configuring multi-tenant specific SMTP settings for email events triggered by the Identity Server.