Hello Mark,
Thank you for posting question on Microsoft Windows Forum!
Based on your query of snapping email to the same grid when one being opened each time. The suggestion here is to use FancyZones (PowerToys). If you want a permanent grid that windows "stick" to. Download Microsoft PowerToys and open FancyZones. Create a layout (grid / custom zones) with the Editor (Edit zones). You can create a custom grid on your monitor (e.g., a "Reading Zone" on the right 40% of your screen). In FancyZones → Window behavior, enable “Move newly created windows to the last known zone” This makes newly opened windows try to reopen in the same zone they were last in. On the other hand, you can hold Shift while dragging an email window, and it will snap perfectly into that pre-defined zone every single time. You can consult this article https://learn.microsoft.com/en-us/windows/powertoys/fancyzones for more information.
Other option is to use Reading Pane which keeps emails "snapped" to the same location is to stop them from opening in new windows entirely. In Outlook: Go to the View tab > Reading Pane > Select Right or Bottom. Now, when you click an email, it appears in a fixed grid on the screen instead of a floating window.
In case, you prefer opening emails in their own windows but want them to automatically go to the same spot. Open an email window. Press Windows Key + Left/Right Arrow to snap it to a specific half of your screen. Windows usually remembers the last size and position of a window "class." If you snap an email window, close it, and then open a new one, Windows should attempt to launch it in that same snapped position. This method is fast but it will not force newly opened windows to always appear there every time.
Hope the above information is helpful! If it helps you getting more insight into the issue, It is appreciated to consider clicking "Accept Answer". Should you have more questions, feel free to leave a message.