There used to be a 'Delete All' button at the top left of my email account. It's now gone. 99.9% of the emails I get on this account are just garbage and I want to be able to choose more than one email to delete at a time. I used to be able to do that, and you keep changing things on email accounts and I now have to look at each email individually to be able to delete them. I don't have that kind of time. How do I select all and then pick and choose those I want to keep?
If I'm reading you right, right-click on the Inbox, or click on the "hamburger" icon to the right when it's selected, then in the menu that pops up click on "Delete all messages". But if there are any you want to keep, create a folder for that and move those there first, then do the mass deletion.