I have some really weird auto-correction issues in Office for Mac (not sure if this also happens in other apps, as I am primarily using Office for texts).
The auto-correction changes of the to oft he and for that to fort hat. There are also other examples, but those are most common and irritating.
The system-wide auto-correction is disabled (in System Preferences -> Keyboard -> Text):
The Autocorrection setting in Outlook is also disabled:
I use Grammarly in Chrome, but it should not affect any system applications.
I noticed that this become more notorious once I added German and Russian to my keyboard layouts. It also had happened before, but it wasn't that irritating. Can it be somehow related? That would partially make sense, as oft is a common German word, but the auto-correction happens while I am using the US keyboard layout, not German (that I rarely use).
Best Answer
I know this is an old post, but I think I may just have figured it out. I am using Outlook on PC, but I have had the exact same issue, such as "for the" becoming "fort he".
I have German and English languages installed and I believe this is the source of the problem (and it goes back at least 14 years if you try Google. Good bug fixing MS).
Anyway, the solution I found was to turn off "Detect Language Automatically" in the email editor. In the PC version this can be found on the Review ribbon under Language. I hope the Mac version has a similar layout.
This has appeared to work so far. It's a pain because changing languages in email will require a manual flip each time, but if I can avoid oft he, fort he, fort hat, etc. then it is worth it.
Hope this helps, even so late after the fact!