What options do I have if I want to send a notification from my APS package to a customer/user?
You can pass the environment variable
'SETTINGS_user_email' to configuration script. Such variable can be defined by service settings declaration in APP-META.xml as follows:
<group class="email"> <setting id="user_email" class="value" type="email"> <name>Primary email address</name> </setting> </group>
You can review the sample application SampleAPS1.2Package-1.2-1.app.zip. This package has defined 'user_email' setting. In the same manner you can pass the SETTINGS_admin_email variable.
Or in APS 1.x we have classes to tell APS controller which data should be used to automatically populate a setting, for example class="login" provides service user's e-mail, class="given-name" provided the name from the contact.