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I had this issue a few weeks back, and it resolved itself. Must have been an issue with O365. BTW, why are you still using 2010 if you have O365?
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1) If you are an Admin in O365 please check if your tenant is impacted by any issue relating to EWS / OOF or any Outage.<br />
(I don't see any issue at this time i.e 22-Feb-2019 at 7 PM India Standard Time. My tenant is hosted in Asia)<br />
I see the following HOWEVER it doesn't seem to apply to your issue.<br />
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MO173811 - Error when loading Office apps<br />
Title: Error when loading Office apps<br />
User Impact: Users may experience errors and app closures when loading any Office 2013, Office 2016, or Office 365 desktop apps.<br />
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More info: Specifically, users may see an error message that states: &quot;We're sorry, but Office App has run into an error that is preventing it from working correctly. Office App will need to be closed as a result. Would you like us to repair now?&quot;<br />
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So i would suggest checking the O365 Health section for more details.<br />
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2) Are you able to send / receive emails? (test In Outlook client and OWA.)<br />
3) Are you able to access you mailbox in OWA ? More importantly can you set OOF here?<br />
4) Check if Auto-discover request is completing in client or not. <br />
Hold CTRL key then right click Outlook icon in the system tray.<br />
Then Test Email AutoConfiguration.<br />
Key in your credentials. Un-check Use Guessmart &nbsp;and Secure Guessmart.<br />
Let it run does it complete?<br />
if yes then click on XML tab.<br />
Review the EWS section and try accessing the URL.<br />
5) Run a (Telerik) Fiddler tool while trying to set OOF. Are you getting 200 or any other error code for OOF URL's<br />
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You might need to reach out to MS Support on this if you are getting Weird IIS web error messages(Fiddler) or if Auto-discover itself doesn't complete.
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Karen,<br />
To clarify, this is a user who has been using Office 2010 with Outlook for a good while and wanted only to move their email to the Office 365 hosted email system. They are only using the email system and not the complete Office 365 package. They have 20+ users but only 1 is experiencing this issue.
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I know. that is exactly what happened to me a few weeks back.
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<div class="content wysiwyg-content">
<a href="https://filedb.experts-exchange.com/incoming/2019/02_w08/1413024/OOF-Error.JPG" target="_blank" title="Screen capture of error message (20 KB)"><img alt="Screen capture of error message" class="file-block lazyload" style="max-width: 626px;" data-src="https://filedb.experts-exchange.com/incoming/2019/02_w08/1413024/OOF-Error.JPG" /></a>Automatic replies (out of office) says server unavailable in Outlook 2010 client with Office 365 Hosted Exchange
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OOF-Error.JPG

Automatic replies (out of office) says server unavailable in Outlook 2010 client with Office 365 Hosted Exchange

Microsoft Office is an integrated suite of applications that includes Outlook, Word, Excel, Access, PowerPoint, Visio and InfoPath, along with a number of tools to assist in making the individual components work together. Coding within and between the projects is done in Visual Basic for Applications, known as VBA.

Microsoft Office

Office 365 is a group of software plus services subscriptions that provides productivity software and related services to its subscribers. Office 365 allows the use of Microsoft Office apps on Windows and OS X, provides storage space on Microsoft's cloud storage service OneDrive, and grants 60 Skype minutes per month. Office 365 includes e-mail and social networking services through hosted versions of Exchange Server, Skype for Business Server, SharePoint and Office Online, integration with Yammer, as well as access to the Office software. All of Office 365's components can be managed and configured through an online portal; users can be added manually, imported from a CSV file, or Office 365 can be set up for single sign-on with a local Active Directory using Active Directory Federation Services.

Microsoft 365

Microsoft Outlook is a personal information manager from Microsoft, available as a part of the Microsoft Office suite. Although often used mainly as an email application, it also includes a calendar, task manager, contact manager, note-taker, journal, and web browser.