I have exchange 2010 and use outlook 2016. One workstation that has 2 email addresses added to outlook has lost connection to the secondary email address. Both email addresses are domain email addresses (firstname.lastname@example.org, userB@domain.net) The workstation operating system is windows 10 pro and is joined to our domain. The user logs on to their domain account and opens outlook. Outlook prompts for the username and password of the second email address but does not allow access to the second email address. Outlook will continue to prompt for the username and password of the secondary email address even after the correct password is entered. Other users on the domain have access to the secondary email address and do not have the connectivity issue. Clicking on the email address in outlook, it says. The set of folders could not be opened. The attempt to logon to Microsoft exchange has failed.