Exchange Server 2010 to 2016 migration

Whenever I add the dummy account to my outlook, everything works as it should - but as soon as I close outlook and open it again, Outlook cannot access the information store anymore. When I check the connection status right after adding the dummy email account, it shows those mapi over http connections

Make sure your Outlook version is latest and supported: Supportability for Mapi over HTTP.

At the same time, try to create a new profile for your mailbox and see if there is any difference.

There is a certificate warning, since currently this is the self-signed certificate from the installation.

What's the description of the certificate warning?

The common cert warnings happened in Outlook are the following:

1 - The security certificate was issued by a company you have not chosen to trust.

If you are using the self-signed certificate for IIS, this cert will not be automatically added to the trusted root certificate store, you should manually trust it by clicking the button "View Certificate" and "Install Certificate" on your clients.

More details about the self-signed certificate: Self-Signed Certificate

2 - The security certificate has expired or is not yet valid.

Click "View Certificate" and view its valid time, if it's expired, renew it and restart IIS.

3 - The name on the security certificate is invalid or does not match the name of the site.

This warning normally is related with the internal/external hostnames of the virtual directories/services(e.g. MAPI, Outlook Anywhere, SCP) and the domain names included in certificate.

Please run the following commands to view if the configurations of them are proper (Please change the value of the parameter -Identity for the cmdlet Get-CasMailbox with your mailbox identities, and don't forget to alter any sensitive info.):

Start-Transcript -Path C:\log.txt
Get-OabVirtualDirectory | fl Identity, server, *Auth*, InternalURL, ExternalURL
Get-WebServicesVirtualDirectory | fl Identity, server, *Auth*, InternalURL, ExternalURL 
Get-OutlookAnywhere | fl Identity, server, *Auth*, InternalHostName, ExternalHostName 
Get-OwaVirtualDirectory | fl Identity, server, *Auth*, InternalURL, ExternalURL 
Get-ClientAccessServer | fl Identity, Name, AutodiscoverServiceInternalUri 
Get-EcpVirtualDirectory| fl Identity, server, *Auth*, InternalURL, ExternalURL 
Get-ActiveSyncVirtualDirectory | fl Identity, server, *Auth*, InternalURL, ExternalURL
Get-MapiVirtualDirectory | fl Identity, server, *Auth*, InternalURL, ExternalURL 
Get-PowerShellVirtualDirectory | fl Identity, server, *Auth*, InternalURL, ExternalURL 
Get-ExchangeCertificate | fl Identity, FriendlyName, Subject, CertificateDomains, Services, Issuer, *not*, Status
Get-OrganizationConfig | fl MapiHttpEnabled
Get-CasMailbox -Identity <User> | fl MapiHttpEnabled
Stop-Transcript