Fix Exchange HTTP Error 503. The Service is Unavailable?

Ashwani Tiwari | Modified: 2020-05-07T13:28:30+00:00 | News, Tips, Windows|

When an Exchange Users / Administrator tries to access the account via OWA (Outlook Web Access) and not able to access the mailboxes due to HTTP Error 503 in Exchange 2013 and Service is unavailable. In this section we mentioning some tips to fix the issues, as various factors can lead to error.

When a request comes from the client to the server, so many operations becomes performed before sending the response to the client. This all is done by IIS (Internet Information Services). It is one of the most powerful web servers provided by Microsoft that is utilized to host the user’s ASP.NET Web application. IIS uses its own ASP.NET Process Engine to manage the ASP.NET request. Hence, when a request comes from the client to server, IIS takes this request then, process it and send back the response to clients. This is how IIS process the request.

However, sometimes IIS stops working due to which Web site no longer takes the requests on all of its bindings. It prevents all subsequent requests from being accepted by applications in the Web site. The new connection to Web site starts failing as if it did not even exist. In this case, when users try to connect via https (ECP/ OWA) or MS Outlook (within the network), they get error Exchange 2013 ECP HTTP error 503, service is unavailable.

Query1: While attempting to connect Remote Web Workplace, Outlook Web Access, Companyweb, or any similar web applications, the site becomes fails to load it. And throws the following error AFTER logging in (onsite and remotely).
Query2: Getting error HTTP 503 due to Security Certificate and not able to open to Exchange Toolbox. Please advise.

Sometimes, the user also may get just a blank page and it all depends on the browser and cache status. Now, users cannot even sync phones either and the Management Shell also does not gets opened. This issue occurs due to IIS Configuration.

Fix Service is Unavailable – HTTP Error Code 503 In Exchange 2013

If the application pool, which is integrated with the web application does not get started ‘HTTP Error 503’ occurs. In order to fix this, follow the steps given below:

1. Open Event Viewer and view the System log to get the errors from Microsoft-Windows-WAS source. Just after that, an event is logged in the System log if the application pool becomes failed to start.

2. In case, if you are not getting any relevant events in the System log then, try to search the relevant entries in HTTPERR log file. You can get the httprr1.log in the following location:


In this file search on “503” to find the relevant information about why application pool failed.
Let us consider a scenario that you have got the following entry:

2011-12-08 18:26:42 ::1%0 6721 ::1%0 443 HTTP/1.1 GET /owa 503 3 N/A SharePoint+Web+Services+Root

The log entry must list the site that you are trying to browse and the application pool, which is being utilized. Here, ensure that the right application pool is being utilized for the site. Suppose, you are trying to browse the “/owa” website via the Sharepoint Web Services Root application pool. Here, it is considered that OWA application is using the MSExchangeOWAAppPool application pool. But, there is a misconfiguration in the Internet Information Services (IIS).

Now, to fix this problematic situation, you need to check the Application Pool for the site and site bindings to verify that IIS is configured properly. It involves the following steps:

  • Launch the IIS Manager MMC. To begin the IIS Manager from Administrative Services console:
  • Click on the Start menu and select All Programs >> Accessories >> Run
  • Now, in Run text box search for the control panel and click OK
  • In Control Panel wizard, select Classic View and hit a double-click on Administrative Tools
  • In Administrative Tools page, hit a double-click on the Internet Information Services

Check HTTPS Port Settings

Analyze the bindings for all websites to verify that they are matching with the default settings that are defined in the following table:

Check Settings

After this, check all Application Pool value to verify that the settings are accurate. Below is the table that contains the default settings for standard SBS application pools.

Check Port Details

Change Settings In ISS Manager

To fix Exchange 2013 HTTP error 503. the service is unavailable,  Provide the Correct Certificate Binding Port to IIS (Information Internet Store ). For that open “ISS manager” and follow the steps:

  • To Open “ISS Manager”, Type “inetmgr” in “RUN” and select Default Web Settings and Open “Edit Binding option”.

Site Binding

  • Now Select Port “443”.


  • Check the SSL Certificate setting and assigned to “Microsoft Exchange”.

Check Settings

  • Similarly, check for Port “444” to Change and View Settings

  •  After checking the Configuration of APP pools mentioned in the first method recycle them in IIS manager.

Restart ISS Manager


While trying to browse the Windows SBS websites, users may get ‘Exchange  2013 HTTP ECP / OWA Error 503 The Service is Unavailable’ . But, resolving this error is not an easy task so there are multiple users who are searching for ‘how to resolve HTTP Error 503 Code in ExchangeService is Unavailable issues. If you are one of those users who is acquiring the same issue then, this blog is for you. Here, we have comprised all information about this error code along with its causes and solution.

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