The description of program setting is given on basis of version 17.0 Choose "Preferences..." item in "Edit" menu. Select "Mail & Newsgroups -> Mail Servers" branch in appear "Preferences" window as shown in picture. Replace "Outgoing mail (SMTP) server" value by 127.0.0.1 Press "OK" button and that is all! Now you can send the test message.

Notes:
1.If you replace TCP port of ADR server from 25 by any other, e. g. 26, then point port by colon - localhost:26.
2.If you use SSL or TSL protected connection then you must switch off protection by choose "Never" as shown in picture. ADR doesn’t support protected connection.