sp_send_dbmail usage best practice
SQL Server core licenses are expensive: using a SQL Server machine's CPU to send thousands of emails has no justification, especially when there are countless better options in terms of features, manageability, setup, troubleshooting.

Another point is that tight coupling between the email and database features makes the application difficult to scale, isolate and manage. One server - one service.

Database mail, in my opinion, should be used for administrative purposes only (alerting) and not for sendind business email messages.