Default SMS App (KitKat)
Android 4.4+ (KitKat) brings with it the idea of a "Default SMS App". The default SMS app is responsible for saving received messages and making other changes to the message database. Any other sms app which is not the default sms app can only read (ie. "see") the messages, but cannot make any changes.
If running 8sms on Android 4.4+, you probably want to set 8sms to be the default sms app so that it can operate properly.
If 8sms is not the default app, many of its functions (such as sending messages and notifications) are disabled because restrictions by Android prevent 8sms from operating fully.
For previous versions of Android older than 4.4, 8sms had a "Stand-alone" mode setting. This is no longer applicable under Android 4.4+ and is made obsolete by the "Default SMS App" setting.