With SMTP, your app communicates directly with the mail server. Some databases do have an email stored procedure. They are useful for simple text only messages from triggers or your own stored procedures.
SMTP is listed as a future feature for PB 2022-R2/R3 so we have that to look forward to. The roadmap doesn't actually say SMTP but it seems to be the only way to implement what it does say:
• Native email client
Enable direct connection to mail server for email services.