Hi there,

You can use Outlook's built-in Advanced Find feature:

1. Select the mail folder, then click on the Search input box, and select Search Tools > Advanced Find.



2. In the pop-up dialog, go to the Query Builder tab, then click Field > User-defined fields in folder, and select the filed your custom field.



3. At last, set Condition and Value, and then Add to List, and click Find Now.



Amanda