IBM iNotes user is not redirected to his mail file after typing in user name and password at the logon prompt. The logon prompt just repeats in a loop. This issue can happen to any application hosted on the Domino Web Server
In a web server environment where "Multiple Server (SSO)" had been selected in the Web Server internet site document on the IBM Domino Server's Server Document >> Domino Web Engine >> Session Authentication field.
When using "Multiple Server (SSO)" The DNS Domain used in the URL on the browser much match the DNS Domain specified in the Web SSO Configuration document. If the URL is not using the same DNS Domain, this loop is expected.
Resolving the problem
Option 1) Change the URL used in the browser to use a host with matching DNS Domain.
Option 2) If this is a single web server environment, this issue can also be resolved after changing the Session Authentication field from "Multiple Server (SSO)" to "Single Server"