No external URL is available to access this mailbox with Exchange ActiveSync

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I have been assigned a task to fix the issue of ActiveSync where Users were able to access their emails on Mobile devices when they are on internal network as soon as they use internet to access the emails, it stopped working. So as starting point of trouble shooting , I checked with Microsoft Remote connectivity analyzer and found the following error .

No external URL is available to access this mailbox with Exchange ActiveSync. Your Exchange server configuration needs to be changed to allow access.

This error is simple pointed to external url of AutoDiscover virtual directory  where external url was empty as expected.

Exchange Version : Exchange 2019 | Client Devices : iOS & Android

Solution 1 :

Add External AutoDiscover url in Virtual Directory. You can run the following command on Exchange Powershell to make it correct.

Set-ActiveSyncVirtualDirectory -Identity “ServerName \ Microsoft-Server-ActiveSync (Default Web Site)” -ExternalUrl https://autodiscover.domain.com/Microsoft-Server-ActiveSync

You can check the status of external Url with following command

Get-ActiveSyncVirtualDirectory | fl identity, InternalUrl, ExternalUrl

Don’t forget to restart IIS services.

You can test now, ActiveSync from Internet should work . If it’s still didn’t work, We have to follow the below steps.

Access the location ‘\ Program Files \ Microsoft \ Exchange Server \ V15 \ ClientAccess \ Sync’ and find web.config file.  Please make a copy of web.conf file as a backup in case we need to revert changes.

Open web.conf file in Notepad and find the section

<appSettings>

You will add the below line in this section

<add key = “ExternalProxy” value = “”> </add>      (Note: If you are copying from here them make sure that quotes are correct.)

It should look like this

<appSettings>

<add key = “ExternalProxy” value = “”> </add>

    <add key=”UserWorkloadManager.PermitSynchronousTaskExecution” value=”false” />

    <!– Config file for tracing –>

Once again restart IIS services and Run Microsoft Remote Connectivity Analyzer , it should work fine now.

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