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Does this issue occur if you use a different exchange account on that iMac?
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Does this issue occur if you use a different exchange account on that iMac?

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Honestly I have not tried but I will try it.
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Honestly I have not tried but I will try it.

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I'm having issues with one particular iMac which is running Yosemite and Outook 2011, basically Outlook was working fine with an Exchange account until 12/30/15, no more emails after that date, so I've removed the account and tried to re-configure it, then more problems, it does the autodiscover but it fails with the following messages: &quot;authentication failed, check your account information and try again&quot; followed by another message &quot;mail could not be received at this time. the server for the account ***** returned the error &quot;logon failure: unknown user name or bad password, your username password or security settings may be incorrect&quot; &nbsp;Would you like to try re-entering your password?&quot; So I'm pulling my hair off, I have tried to rebuilt the identity or to even create a fresh identity but nothing worked. The information entered is completely correct, I have used the same username and password over and over on my PC Outlook, iPhone and OWA browser and it works every time. Please help, not sure where to go from here. The account works just fine on a different MAC.
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I'm having issues with one particular iMac which is running Yosemite and Outook 2011, basically Outlook was working fine with an Exchange account until 12/30/15, no more emails after that date, so I've removed the account and tried to re-configure it, then more problems, it does the autodiscover but it fails with the following messages: "authentication failed, check your account information and try again" followed by another message "mail could not be received at this time. the server for the account ***** returned the error "logon failure: unknown user name or bad password, your username password or security settings may be incorrect"  Would you like to try re-entering your password?" So I'm pulling my hair off, I have tried to rebuilt the identity or to even create a fresh identity but nothing worked. The information entered is completely correct, I have used the same username and password over and over on my PC Outlook, iPhone and OWA browser and it works every time. Please help, not sure where to go from here. The account works just fine on a different MAC.

MAC Outlook 2011

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.

Outlook

Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.

Exchange

Mac OS X is the desktop operating system from Apple Inc., found on Macintosh computers. OS X consists of a Mach/BSD-based kernel, operating system interfaces primarily based on FreeBSD and additional frameworks (written in C, C++ and Objective-C providing user interface and application-level services.