Which activity can be used to retrieve only unread messages?

The activity that retrieves only unread messages is the one that specifically has the capability to filter emails based on their read status. In the case of the option related to Outlook, the 'Get Outlook Mail Messages' activity is designed to connect to the Outlook application and offers various filtering options, including the ability to specify that only unread messages should be fetched. This makes it particularly useful for scenarios where you want to process new or unread emails without having to sift through those that have already been read.

The other options are less focused on this specific requirement. For instance, 'Get All Mail Messages' typically pulls in every email from the specified account, regardless of whether they’ve been read or not. Similarly, 'Get IMAP Mail Messages' and 'Get POP3 Mail Messages' do not inherently filter for unread emails unless additional logic is implemented after retrieving the messages. Therefore, the option that allows for the direct retrieval of unread messages is the most efficient and precise choice among the options provided.