Is there a way to select all emails in Mail app and mark as read?

If you go to Mail, then the Inbox of the account in question. In the upper right corner, tap on Select. Then on the upper left you should see Select All. After you do that, you should see a blue checkmark by each mail listing. Go to the bottom left corner of the screen, tap on Mark, then select Mark as Read.

USAFA68 wrote:

As pointed out to me several times by Apple tech support guys, in the latest iOS, there is no Select All button in upper left or elsewhere. It used to be there, but no longer. I do not want to mark individual emails as READ, I want to group them as Select All...but cannot.

Well, I've would not have indicated that choice was there if it wasn't on my iPhone. I've attached a screenshot showing the Select All button. And, you said that wanted to mark them as Read in your original post.

I am on the latest, iOS 18.2. None of it is beta software, it is all public release. Maybe someone else will look at this and add some information, but mine has been this way. And to be honest, your Outbox should only appear if there is mail waiting to send. Once mail is sent, the Outbox disappears. It is a temporary folder.