Here is how to disable Autocorrect or Spelling Check Feature in Windows 10. This disables Autocomplete feature even if you are using mail app.
Method 1 – Using gpedit.msc
1. Press Windows key + r together to open run.
2. Write gpedit.msc in it and click OK.
3. Now, go to the following path in left side of gpedit pane.
User Configuration -> Administrative Templates -> Control Panel -> Regional and Language Options
4. Now, click to enable both Turn off autocorrect misspelled words and Turn off highlight misspelled words
Method 2 – Using settings
1. Click on start button.
2. Click on gear shaped icon to open settings.
3. Click on Devices.
4. Click on Typing from the left panel.
5. Toggle off Autocorrect misspelled words Option.