Hello Henry,
Deleting unwanted emails is a good practice and put impact on your entire data’s size but not at an extent volume. Even, after deleting unwanted emails, white spaces persist in the PST File.
So, along with deleting emails, use compact feature to eliminate these white spaces in MS Outlook.
To do so:
Open “MS Outlook” >> “File” tab >> “Account Settings” >> “Account Settings” >> “Data File” >> Click twice on PST File >> Click on “Compact Now”
Feel free to ask further!!!
Thanks & Regards
Michael Scofield