Error: ORA-29278: SMTP transient error: 421 service not available

What's Causing This Error

This error usually occurs when the SMTP server is not accepting the socket connection call. The most common reason is when the SMTP server does not have an SMTP server running on the specified port.

Solution - Here's How To Resolve It

To resolve this issue, the user must ensure that the SMTP server accepts connections and that a valid SMTP server runs on the specified port. The system administrator of the SMTP server can provide the correct SMTP connection information required by the client.