OCI: Unable To Send Mail Through OCI Email Delivery, Failed With Error "DSN: Service unavailable"

Applies to:

Oracle Cloud Infrastructure - Version N/A and later

Information in this document applies to any platform.

Symptoms

Configured email delivery service and configured Sendmail to Send Email Through Email Delivery but mail delivery fails with following error.

Mar 2 09:45:34 localhost sendmail[8448]: STARTTLS=client, relay=smtp.email.me-xxxx-1.oci.oraclecloud.com., version=TLSv1/SSLv3, verify=FAIL, cipher=DHE-RSA-AES256-SHA256, bits=256/256
Mar 2 09:45:34 localhost sendmail[8448]: 1229jYGo008446: to=<testuser@externaldomain.com>, ctladdr=<opc@localhost.xxxx.localhost.oraclevcn.com> (54322/54323), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=120396, relay=smtp.email.me-****...i.oraclecloud.com. [x.x.x.x], dsn=5.0.0, stat=Service unavailable
Mar 2 09:45:34 localhost sendmail[8448]: 1229jYGo008446: 1229jYGo008448: DSN: Service unavailable
Mar 2 09:45:34 localhost sendmail[8448]: 1229jYGo008448: to=<opc@localhost.sub10301306531.localhost.oraclevcn.com>, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=31681, dsn=2.0.0, stat=Sent