Actually, you can easily delete multiple or all emails with hotkeys in Outlook. Please do as follows:

Open the specified mail folder you will delete emails from, select multiple or all emails, and press the Delete key to remove them (or press Shift + Delete keys together to permanently delete them).

Tips for selecting multiple/all emails:
(1) Holding the Ctrl key, you can select multiple nonadjacent emails with clicking them one by one;
(2) Holding the Shift key, you can select multiple adjacent emails with clicking the first one and the last one.
(3) Select any one of emails in the mail list, and then press Ctrl + A keys together to select all emails in the mail folder;
(4) Select the first email in the mail list, and then press Ctrl+ Shift + End keys together to select all emails.

One click to delete all duplicate emails from a mail folder in Outlook

Provided by Kutools for Outlook!

With the Archive feature, you can not only delete multiple or all emails from the specified mail folder in Outlook, but also store these deleted emails on your hard discs.

1. Click File > Info > Tools > Clean Up Older Items (or File > Info > Cleanup Tools > Archive) to open the Archive dialog.

2. In the Archive dialog, please do as right screenshot shown:
(1) Check the Archive this folder and all subfolders options;
(2) In below list box, please select the specified folder you will remove emails from;
(3) Into the Archive items older than box, please type the date that you will remove emails by. (For removing all emails, please type Tomorrow into it);
(4) Click the Browse button.

3. In the Open Outlook Data Files dialog box, please type a name for the new archived PST file in the File name box, and click the OK button. See screenshot:

4. Now you return to the Archive dialog, please click the OK button.

Note: If any dialog pops out to reminder you, please click the Yes button to go ahead.

So far, all emails you modified before the specified date have been removed from the certain folder in Outlook.

For deleting multiple emails by sender or subject, you can apply Kutools for Outlook’s (Delete Mails) By Sender or By Subject feature to get it done.

1. In the Mail view, select the email whose sender (or subject) you will delete email by, and click Kutools > Relative Current > By Sender (or By Subject). See screenshot:

2. In the popping out dialog, please specify the deleting scope in the Filter Conditions section, and then click the Delete button. See screenshot:

3. And now a dialog box comes out and tells you how many emails have been deleted. Please click the OK button.

So far, all the emails which have the same sender or subject  in the current opening mail folder have been deleted at once.

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