You can find out all unread emails with the Instant Search feature in Outlook, select all search results, and then delete them easily.

1. In the Mail view, click to open the mail folder you will delete all unread emails from.

2. Press Ctrl + E keys simultaneously to activate the Search Tools, and then click Search > Unread. See screenshot:

Note: You can also change the search scope in the Scope group on the Search tab.

3. Now all unread emails are found out and listed in the mail list. Select the first search result in the mail list, and then press the Ctrl + Shift + End keys to select all search results.

4. Press the Delete key to remove all found unread emails.

Automatically or bulk mark all deleted unread emails as read in Outlook

Sometimes, you may delete spam emails directly before reading them. However, these emails keep unread status in the Deleted Items folder. It will be boring to show the number of unread items besides the folder on the Folder pane. Here, Kutools for Outlook released a Mark (Deleted) As Read feature to:

A. One click to mark all deleted unread emails as read in the Deleted Items folder, including or excluding all subfolders;
B. Automatically mark every unread email as read once it’s deleted and moved to the Deleted Items folder.

You can also find out all unread emails with the Filter Email feature in Outlook, and then easily delete all filtered out unread emails.

1. In the Mail view, click to open the mail folder where you need to delete all unread emails.

2. Go ahead to click Home > Filter Email > Unread.

And now all unread emails have been filtered out in the current mail folder.
Note: You can also change the filtering scope within the Scope group on the Search tab.

3. Select the first filtered out unread email, next press the Ctrl + Shift + End keys to select all unread emails, and finally click the Delete key.

And now all unread emails are removed from the specified filtering scope.

You can also collects all unread emails within a search folder, and then remove all unread emails at ease from the search folder.

1. Select the email account where you will remove unread emails from, and click Folder > New Search Folder. See screenshot:

2. In the opening New Search Folder dialog box, click to select the Unread mail option, and click the OK button. See screenshot:

An unread search folder has been created and added on the Navigation pane. All unread emails will display in the unread search folder automatically.

3. Click to open the unread search folder, and select all unread emails in the mail list. See screenshot:

Note: There are two ways to select all emails in the mail list:
(1) Click any one of emails in the mail list, and then pressing the Ctrl + A keys at the same time;
(2) Click the first email in the mail list, and then press the Ctrl + Shift + End keys simultaneously.

4. Press the Delete key to remove all selected emails.

And now all unread emails are removed from the Inbox folder immediately.

Automatically bold or not bold unread messages in Outlook

Highlight unread (new incoming) email messages in Outlook

Show the number of unread items including subfolders in Outlook