Realme's realme UI may require additional setup for notifications to work as intended for apps, including Aqua Mail. To ensure the best possible notification delivery check the following options:
Android Setings > App management > App List > Aqua Mail > Data usage details > Background data > Allow
Android Setings > App management > App List > Aqua Mail > Battery usage > Allow background activity > Allow
Android Setings > App management > App List > Aqua Mail > Battery usage > Allow auto launch > Allow
Android Setings > App management > App List > Aqua Mail > Manage Notifications > Allow notifications > Allow
Recent apps menu > Aqua Mail > Options > Lock
Guide created with realme UI 2.0 / Android 11. Please note some setting names and locations may differ depending on your realme UI version and device model.