ResenderOPPO: SMS forwarding stops in the background
ColorOS, the system on OPPO phones, freezes apps that are not on screen to save battery. An SMS forwarder lives in the background by definition, so without two switches Resender works while you look at it and sleeps when you don't.
The two switches
- Open Settings → Apps → Resender → Battery usage.
- Turn on “Allow background activity”.
- On some phones, also turn on “Allow auto launch” (Settings → Apps → Auto launch; on older versions Settings → Battery → App auto-launch).
- Allow background activity. Settings → Apps → Resender → Battery usage: allow background activity (on some versions the choice is called Allow background running or Unrestricted). This is the switch that keeps Resender alive when you leave it. On ColorOS 16 the same screen offers three choices instead of a switch — Allow background activity, Smart mode (Recommended), Restrict background activity: choose the first; on ColorOS 15 the Optimize battery use line below switches to Don't optimize by itself once background activity is allowed.
- Allow auto launch. Settings → Apps → Auto launch on newer versions, Settings → Battery → App auto-launch or Settings → Apps → App management → Resender → Auto launch on older ones: switch Resender on. Without it, the system does not start Resender after a restart or when an SMS arrives while it is not running.
Then take Resender off Android's own battery optimisation: the app's main screen has a button that opens the system list — find Resender and choose Don't optimize. ColorOS also has a list of its own: Settings → Battery → Advanced settings → Optimize battery use — set Resender to Don't optimize there; the default is Always ask.
How to check it worked
Lock the phone, wait a minute, and send it an SMS from another phone. The email should arrive within seconds. If it arrives only after you unlock the phone or open the app, one of the switches is off — after a ColorOS update, check both again.
What no app can do
ColorOS's battery screens have no public interface. No app can read them, change them, or tell whether you have set them. Resender shows a red line when Android reports that it is being restricted and opens the right system screen for you — the switches are yours. Skip them, and messages arrive late or not at all while the app has done everything it is allowed to do.
Questions
Messages arrive only when I open the app. Why?
ColorOS freezes apps that are not on screen unless they are allowed background activity and auto-launch. Resender gets the SMS only when the system lets it run again — hence the delay. Set the two switches on this page once.
I cannot find Auto launch.
Its home moves between ColorOS versions: Settings → Apps → Auto launch on ColorOS 13 and newer, Settings → Battery → App auto-launch or Settings → Apps → App management → Resender → Auto launch on older ones, or inside the Phone Manager app under Privacy permissions → Startup manager.
Is the Android battery-optimisation switch also needed?
Yes. Resender's main screen has a button that opens the system list: find Resender and choose Don't optimize. ColorOS's own list: Settings → Battery → Advanced settings → Optimize battery use → Resender → Don't optimize.
Why doesn't Resender switch these settings itself?
ColorOS's screens have no public interface: no app can read or change them. The one Android setting an app could change with a single dialog needs a permission Google Play grants only to alarms, calling and similar categories, which a message forwarder is not.
Are realme and OnePlus the same?
Nearly: realme UI and recent OxygenOS are built on ColorOS, so the switches are the same and only the menu names differ. Each has its own page here.