Hi Peter,
The Wazuh Indexer and Wazuh Dashboard started out as forks of Opensearch and Opensearch dashboards.
As such they give you all the functionality of those products as well as the SIEM and XDR features of Wazuh on top of that.
We usually suggest using Wazuh's built- in e-mail functionality as it is easier to set up and configure:
Unless you have any specific requirements that go beyond the capabilities of the e-mail module, our recommendation is to just use that one.
Let me know if my answer helps clarify things.
Regards,
Fede