After upgrading a database to 11gR trying to send emails using UTL_SMTP fail with
Starting with Oracle 11g "fine-grained access" was implemented to limit usage of packages like UTL_SMTP, UTL_HTTP connecting over the network to other services like mail server etc.
By default, the ports are blocked and ORA-24247 is raised to signal this.
To control the ACL, Package DBMS_NETWORK_ACL_ADMIN can be used to create ACL and grant access to particular user.
Bingo, it works now!