Hi Customer,
Welcome to the Microsoft Community. Thank you for posting into the forum community.
From your mentioned description, can we re-confirm and collect below information from your side for further analysis?
1. Could you please provide us detailed screenshot page of Office version? To know version > open Outlook > File > Office Account and provide us entire page screenshot?
2. Could you please provide us detailed screenshot about “certain names on individuals that email me are automatically added to Roamigcustom.dic”?
3. Does this issue has happened with other users into the organization?
Meanwhile, I have observed few things from my end. Generally, “Roamigcustom.dic” is default dictionary under Custom Dictionaries on Outlook. So, such name or individual word might be automatically captured from address book.
At initial stage, please try to delete one or two individual words from the roamingcustom.dic via selecting “Edit Word list” option and identify the result after re-starting Outlook. Here is the information article about Add or edit words in a spell check dictionary
Regards,
Darpan