Beginning with Exchange 2013 CU 6, the Exchange 2013/2016 itself performs redirection from the default website to the /OWA virtual directory. That means that if a user goes to https://mail.contoso.com Exchange will redirect the user’s browser to https://mail.contoso.com/owa. But what about http? If a user goes to mail.contoso.com, he expects to be redirected to mail page https://mail.contoso.com/owa.
Technet recommends this way https://technet.microsoft.com/en-us/library/aa998359(v=exchg.150).aspx So you need to configure Redirect request and SSL requirements of the Default Web Site and all virtual directories. Not so simple and you will need to perform this operation after any Cumulative Update installation or certificate change.
I recommend more simple way to implement HTTP redirection on Exchange Servers.
- Open IIS Manager on the Exchange Server and select the server name.
- Double-click Error Pages.
- Click the Add action on the right and create a new error page for status code 403.4 that responds with a 302 redirect to https://mail.contoso.com/owa as shown below.