OpenSMTPd no longer support dsn-notify option
OpenSMTPD no longer recognize the dsn-notify option. It was working fine in Alpine 3.4
If the dsn-notify parameter is used with the disable argument, the listener will not generate DSN upon delivery failures.
See https://www.opensmtpd.org/faq/options.html\#listen
(from redmine: issue id 7588, created on 2017-07-23)