You can use the APEX_MAIL package to send an email from an Oracle Application Express application. This package is built on top of the Oracle supplied UTL_SMTP package. Because of this dependence, the UTL_SMTP package must be installed and functioning to use APEX_MAIL.
Oracle Database PL/SQL Packages and Types Reference for more information about the UTL_SMTP package
APEX_MAIL contains three procedures. Use APEX_MAIL.SEND to send an outbound email message from your application. Use APEX_MAIL.PUSH_QUEUE to deliver mail messages stored in APEX_MAIL_QUEUE. Use APEX_MAIL.ADD_ATTACHMENT to send an outbound email message from your application as an attachment. For complete descriptions of all Application Programming Interface packages for Oracle Application Express, see Oracle Application Express API Reference.
"APEX_MAIL" in Oracle Application Express API Reference and "Configuring Email" in Oracle Application Express Administration Guide