Surely, this is a simple thing and not worthy of StackExchange superuser. But my search in the internet shows only that several other people have this same question, and aren't getting an answer from MS. So, I am trying to use the Outlook web app. How do I check for new messages? The advertised button for doing so just isn't there AFAICT. Thanks.
You don't need to refresh it.
New e-mails appear as soon as they arrive into your mailbox.
(I haven't find any reference for it, however tested and it works like this)