Here's what you do in Outlook.

File > Options > Spelling and Correction > AutoCorrect Options > Auto Correct Tab

Scroll through list at bottom. Find the entries that you don't want auto corrected and delete them. The OP would want to delete IHS an EHR.

Funny, I was having this same issue with those exact same acronyms. Thanks for the info!

I'm less ignorant than I was yesterday.