David works as a Support Analyst for White Well Inc. He uses Microsoft Outlook for messaging and e- mailing. MS Outlook has been configured to use an IMAP account. He has created a custom field…

David works as a Support Analyst for White Well Inc. He uses Microsoft Outlook for messaging and e- mailing. MS Outlook has been configured to use an IMAP account. He has created a custom field Relation that represents the relation between the sender and receiver. He wants to find all e-mails where relation is CEO. He opens the Advanced Find dialog box, clicks on the Advanced tab and then selects the User defined fields option from the drop-down list. However, the Relation field is not available to use. Which of the following is the most likely cause of the issue?