Error "SMTP Port 25 Closed for Outside Communication" When Using SMTP on a Platform as a Service Instance

(Doc ID 2010183.1)

Last updated on NOVEMBER 14, 2017

Applies to:

Oracle Compute Cloud Service - Version N/A and later
Oracle Database as a Service - Version N/A and later
Java Cloud Service - Version N/A and later
Information in this document applies to any platform.

Symptoms

In applications deployed onto Platform as a Service (PaaS) instances, such as IaaS / DBaaS / JaaS,  when trying to communicate via SMTP with external mail servers (outside of the Oracle Cloud), you will see the "SMTP Port 25 Closed for Outside Communication" error.
An example is an Oracle Database database trigger in an Oracle Database as a Service instance (DBaaS) sending out e-mail notifications on certain events happening in the database, with the trigger using the UTL_SMTP PL/SQL package; most likely error "ORA-24247: network access denied by access control list (ACL)" or "ORA-29278: SMTP transient error: 421 Service not available", will be reported.

Cause

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