On the Tools menu, click AutoCorrect.
To prevent Microsoft Graph from automatically capitalizing any word that is typed after an abbreviation, click the First Letter tab, and then type the abbreviation — including the period — in the Don't capitalize after box.
To prevent Microsoft Graph from automatically correcting a word that contains a mixture of uppercase and lowercase letters, click the INitial CAps tab, and then type the word in the Don't correct box.
Click Add, and then click OK.
Exclude specific abbreviations or capitalized text from automatic changes