LanguageTool for Windows offers advanced error detection and style improvements for your writing, which might overlap with the corrections from Window's native spellchecker. This guide will show you how to disable the native spellchecker in Microsoft Outlook, allowing you to concentrate solely on the suggestions from LanguageTool.
Classic Outlook
Open a new message by clicking on “New Email”
In the new email window, navigate to the “Review” tab
Choose “Set Proofreading Language…” from the “Language Select” section
Tick the “Do not check spelling or grammar” checkbox
Confirm your setting by clicking “Set As Default”
Outlook 365
Open a new message by clicking on “New mail.”
In the new email window, navigate to the “Options” tab.
Choose “Editor Settings” from the “Editor” section.
Uncheck all options under the “Corrections” section.
Confirm your settings by clicking “OK.”
With these steps, Microsoft Outlook will no longer display its native spelling and grammar suggestions, allowing you to focus on LanguageTool's advanced grammar and style recommendations in your document.