
Samsung Galaxy Tab A 8.0
Every official firmware build for SM-T350X, newest first: one row per build with all regions (CSC) that received it.
Specifications of SM-T350, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-T350

SM-T357W

SM-T355C

SM-T2558

SM-T365Y
You can find the firmware on the model: SM-T350X page.
Yes, all firmware files for SM-T350X are 100% official, original, and obtained directly from Samsung servers.
To flash SM-T350X, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing SM-T350X.