Hi Jay,
Thank you for your message.
In order to re-generate the Sort/Search Indexes for that specific account, a good method would be to run the below CLI commands:
<#> update domain name <your_domain_name>
+OK: command successful
<domain#> update account <affected_account>
+OK: command successful
<domain-account#> purge disposablemetadata all
Purging disposable meta data
+OK: command successful
<domain-account#>
The best way to speed up the Outlook search is to add the folder of your PST file to Windows Index from Control Panel > indexing Options:
HTH,
Bogdan Maxim