Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi RPGS_h2,
Thank you for posting into the forum community. We will highly appreciated your kind cooperation and patience in our forum community.
Based on your mentioned concern, may I please just double confirm whether your concern is about to expand AutoComplete lists entries or to expand email address auto populate as suggestion under the Outlook?
If your concern is about to expand AutoComplete lists entries, it is application for Outlook 2010, Outlook 2013, Outlook 2016, and Outlook 2019. On the other hand, it is not applicable for Outlook 365. Here is the article for the reference: Information about the Outlook AutoComplete list
Meanwhile, if your concern is about to see auto populate email address list under Outlook 365, currently we can see 5 email addresses as a suggestion lists. At present, it is not feasible to expand auto populate email address limits under the Outlook 365. For more information about Manage suggested recipients in the To, Cc, and Bcc boxes with Auto-Complete
Stay safe and healthy.
Regards,
Darpan