Outlook 2010/2013 and Exchange 2016. Password prompt when computer is outside organiozation

Hi

I've a problem with connection to Exchange 2016 when users are outsite. Inside company (LAN connection) when users run outlook 2010 or 2013 (compuers are in domain of course), there is no problem with connection to server. When they are outside and run Outlook they gets password prompt window. If they fill in password, the conection is established. Users have to change password for every 30 days so they can't use option "Remember password". Is it normal situation?

What is the problem? Please help.

This is mapi virtual directory settings (Get-MAPIVirtualDirectory | fl Identity,*URL*,*Auth*):

Identity                      : Exch1\mapi (Default Web Site)
InternalUrl                   :https://mail.domain123.com/mapi
ExternalUrl                   :https://mail.domain123.com/mapi
IISAuthenticationMethods      : {Ntlm, Negotiate}
InternalAuthenticationMethods : {Ntlm, Negotiate}
ExternalAuthenticationMethods : {Ntlm, Negotiate}

Using Remote Connectivity Analyzer > Microsoft Office Outlook connectivity Tests:

- Outlook Connectivity: test passed

- Outlook Autodiscover: test passed

Kind Regards Tomasz