When you try to create an Outlook profile or connect to a Microsoft Office 365 mailbox, you're continually prompted for credentials while the client displays a "trying to connect..." message. If you cancel the credentials prompt, you receive the following error message:
The connection to Microsoft Exchange is unavailable. Outlook must be online or connected to complete this action.
This issue can occur if the Logon network security settingon the Security tab of the Microsoft Exchange dialog box is set to a value other than Anonymous Authentication.
To fix this issue, change the Logon network security setting to Anonymous Authentication. To do this, follow these steps:
Open Control Panel, and then do one of the following:
In Windows 10, Windows 8.1, or Windows 7, click Start, type control panel in the search box, and then press Enter.
In Windows 8, swipe in from the right side to open the charms, tap or click Search, and then type control panel in the search box. Or, type control panel at the Start screen, and then tap or click Control Panel in the search results.
In Control Panel, locate and double-click Mail.
Click Show Profiles, select your Outlook profile, and then click Properties.
Click E-mail Accounts.
Select your email account, and then click Change.
In the Change Account dialog box, click More Settings.
In the Microsoft Exchange dialog box, select the Security tab.
On the Login network security list, select Anonymous Authentication, and then click OK.
Click Next, click Finish, and then click Close on the Account Settings dialog box.
Click Close on the Mail Setup dialog box, and then click OK to close the Mail control panel.
To locate and view the registry setting for Anonymous Authentication in the Outlook profile, follow these steps.
Important Modifying the Outlook profile by using the "Profiles" registry path is not supported and may cause your Outlook profile to be in an unsupported state.
Important Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you access it, back up the registry for restoration in case problems occur.
Open Registry Editor. To do this, do one of the following:
In Windows 10, Windows 8.1, or Windows 8, press the Windows logo key+R to open the Run dialog box, type regedit.exe, and then click OK.
In Windows 7, click Start, type regedit in the Start Search box, and then press Enter. If you're prompted for an administrator password or for confirmation, type the password, or click Allow.
Locate the following registry path, as appropriate for your version of Outlook:
For Outlook 2013 HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Profiles
For Outlook 2010 and 2007 HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles
Under this subkey, locate and expand the name of your Outlook profile.
Under the profile, locate and expand the 9375CFF0413111d3B88A00104B2A6676 key.
Under the 9375CFF0413111d3B88A00104B2A6676 key, you see a subkey for each account in your profile. Select the first subfolder (00000001), and then examine the data of the Account Name binary value by double-clicking the value. Repeat this process until you find the Account Name value that includes your SMTP address. For example, the Account Name value points to firstname.lastname@example.org under the \00000003 subkey.
Under the \0000000x subkey, locate the Service UID binary value. It represent a GUID (for example, c3 d1 9a 7b 80 1b c4 4a 96 0a e5 b6 3b f9 7c 7e).
Locate the subfolder in your profile that matches the GUID value that's identified in step 6 (for example, \c3d19a7b801bc44a960ae5b63bf97c7e).
Under the subkey that you found in step 7, examine the 01023d0d binary value. It represents a GUID (for example, 5f cf d5 f1 ba 5c 6f 45 b3 57 cc 5e 0d 16 94 58).
Locate the subfolder in your profile that matches the GUID value that's identified in step 8 (for example, \5fcfd5f1ba5c6f45b357cc5e0d169458).
Under the subkey that's found in step 9, examine the value of the 00036619 binary value. This value determines whether Outlook is using Anonymous Authentication.
Binary: 00036619 Data: 01 f0 00 80 == Anonymous Authentication Any other value represents an authentication method other than Anonymous.