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Error 503: Can't connect to exchange server via Outlook mobile

Jona De Sacco
Jona De Sacco used Ask the Experts™
Good morning,

I have a weird error with my exchange server.
Outlook and OWA work just fine. Sending and receiving mails works. The only thing that doesnt work is connecting to the exchange server with Outlook for my phone. Everytime I try to add my mailbox in Outlook it gives me the error-message "The service is currently unavailable. Try again. If the error persists, please contact customer support. (503)"
This error only occurs with Outlook for mobile and other mail apps for the phone.

I've looked through some support forums but haven't found a solution for this problem. Does anybody have an idea what I should do?
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AmitIT Architect
Distinguished Expert 2017

You need to enable Activesync for your account. Your Exchange admin would be able to help you.
Saif ShaikhServer engineer

You might be using IOS device. These issues are likely to happen with IOS devices recent update.

Check the same in Android phone with outlook app installed


Thanks for the answer Saif,

unfortunately I'm using android phones. It doesn't work there either.


Thanks for the answer Amit,

I should have stated this, sorry. I'm not a normal user. The error occurs with the exchange server of one of my clients. I'm not a exchange expert though.

The error is occuring for all users, with any kind of phone or mail app. Doesn't matter if they are connected to the company network or to their wifi at home. I've checked some forums where it stated that the IIS would be the source of the problem but I've checked everything they wanted me to check and everything is how its supposed to be. I didn't find anyone with exactly my problem so thats why I posted the question here.
AmitIT Architect
Distinguished Expert 2017

Please answer below question:

1) Are you trying to setup mobile device first time or it was already there and working in past?
2) If it is first time, you need to configure Active Sync on your server and you also need certificate.
3) If it was already setup and broken recently, first thing you need to ask, was there any change made recently.
4) Next when did you restarted your Exchange server last time. If not recently, give a reboot and test again.
5) For testing you can use exrca.com site from MS. Select Activesync test.


1) It was working in the past. We changed the firewall recently and the problem occurs since then. I checked all the firewall rules though and they are the same like in the other firewall.
4) We rebooted the server just yesterday evening.
5) Did that. This comes as error:
HTTP 403 forbidden. The authenticated user isnt authorised to use the requested ressource.

Cant give you the complete error code since its in german.
IT Architect
Distinguished Expert 2017
I advise you to revert firewall change and test again.