How do I select multiple emails in Trident (Windows)?

To select multiple emails, you can click the sender image displayed in the email list.

Note: If the setting to show sender's photo in list view is off, you can hover over the emails and click the checkbox.

To select all emails that are loaded in the current view, press Ctrl + A.
If you want to select all emails in the entire folder, press Ctrl + A and then click Select all emails in this folder.