Fix BlueMail push notifications on OnePlus

OxygenOS layers two extra optimisations over Android’s, and the one that most often delays mail overnight — sleep standby optimisation — is not in the per-app settings at all.

Set BlueMail to unrestricted

Settings → Apps → App management → BlueMail → Battery usage → Unrestricted (older builds: Battery → Battery optimisation → All apps → BlueMail → Don’t optimise).

Turn off sleep standby optimisation

Settings → Battery → Battery optimisation → ⋮ (three dots) → Advanced optimisation.

Turn off Sleep standby optimisation. It cuts the network while the phone is idle at night, which is why the first mail of the morning often arrives only when you pick the phone up.

Turn off Deep optimisation in the same place if it is present.

Allow auto-launch

Settings → Apps → App management → BlueMail → Allow auto-launch, where your build has it. Without it BlueMail does not restart after a reboot until you open it.

If mail still arrives late

• Lock BlueMail in Recents — OnePlus builds have been known to revert per-app battery settings, and a locked app survives it.
• Re-check these settings after a system update; a major OxygenOS upgrade often resets them.
• Confirm Settings → Notifications → BlueMail is allowed and not silenced.