Configuring Email Notification Oracle 12c

  alerts, email, oracle, smtp, windows

I am trying to create a StoredProcedure that sends mail about the status of% of the tablespaces of an Oracle DB.
However, initially it sends me the following error (ORA-29278: transient SMTP error: 421 Service not available).
ACLs were created, permissions, communication to mail server, port, and firewall were validated, and the error no longer occurs.
The SP appears to be running correctly, but the notification mail is not being received.enter image description here

Source: Windows Questions