If you receive a message on your Huawei device, and it is a MMS, your device will download the attached files automatically. This is activated by default. If you need more control over your data plan, you can also disable this function and download MMS manually.

Note: If this is activated, you will be asked for settings regarding downloading MMS automatically while roaming is active. 

Android 10 | EMUI 10.0
Auto-download MMS -  Open  Messages
Auto-download MMS -  Open the  menu
Auto-download MMS -  Open the  settings
Auto-download MMS -  Tap on  Advanced
Auto-download MMS -  Activate or deactivate  Auto-downloading MMS
  1. Open Messages
  2. Open the menu
  3. Open the settings
  4. Tap on Advanced
  5. Activate or deactivate Auto-downloading MMS

Huawei Instructions