Exchange on prem 2019/2016- mobile outlook connection problem

Question

I have mix on-prem environment exch2016/2019. External client always connect using VPN- on computers and on phones. When I tried connect from outside location (VPN established) Outlook Anywhere working smoothly. When I'm trying connect using phone- Mobile Outlook (VPN established) can't connect- prompting for logon all the times. Everything looks correct- Outlook anywhere from computers correctly connect to mapi folders, HTTP protocol is used, outlook mobile prompting for logon.

Another question- do you know that there is tricky configuration instead of using WAP and ADFS for publishing exchange resources? can I publish resources without WAP and ADFS? All devices connect using VPN for any external connections so proxy doesn't make sense. Nothing is opened directly to the internet

Answer 1

@Robert Szymanski

Do you try to reconfigure a new Outlook profile on your mobile when connecting from the external?

Based on your description, PC could connect to Exchange successfully with VPN, I think the DNS records are correct. This phenomenon may relate to VPN for mobile.

I would suggest you try to test the ActiveSync configuration from this tool on an external computer which connected with VPN. If could test successfully, it means this phenomenon caused by the mobile device cannot find the correct DNS record.

If this tool returns an error, could you provide that error message to us?

You can also try to configure mailbox on the Mail UWP App (Also using ActiveSync to connect with Exchange) on Win 10/11, I also could help us narrow down this phenomenon.

Another question- do you know that there is tricky configuration instead of using WAP and ADFS for publishing exchange resources? can I publish resources without WAP and ADFS? All devices connect using VPN for any external connections so proxy doesn't make sense. Nothing is opened directly to the internet

ADFS could provide a two-way verification for mailbox, it also could be used when VPN down. Just connecting with VPN without ADFS is also ok.

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Answer 2

The main problem is that environment is completely separated and I can't use Exchange Remote Connectivity Analyzer for testing. VPN is required on phone and computer.

On Laptop(VPN Established) Outlook Anywhere working fine but Outlook mobile (VPN Established on mobile) can't find server using Autodiscover and then after manual configuration prompt continuously.

Answer 3

I just made DNS deep debugging and funny is that Outlook Mobile by design trying contact to office 365 addresses and if local network is isolated don't switch to local Exchange Server. ActiveSync working ok, Outlook Anywhere ok. So in this scenario when local Exchange are available only by vpn in my opinion you can't use Outlook Mobile client

Answer 4

Hi Robert, how did you resolve the problem with the connection to your on-prem exchange?