When you use IMAP to connect to your email account in Microsoft Outlook 2016, authentication fails.
This issue may occur because you have a Unicode character in your password, such as one of the following:
To work around this issue, use one of the following methods.
Method 1: Change your password
Change your password so it no longer contains any Unicode characters.
Method 2: Use a different protocol than IMAP
You may be able to configure your email account to use POP3 instead of IMAP if your email server supports POP3 connections. The following steps will create a new Outlook profile that's configured to connect by using POP3.
Note The POP3 protocol downloads email to your local computer and removes it from the server, whereas IMAP leaves a copy of the email on the server. For more information, see Understanding the differences between POP3 and IMAP4.
In Control Panel, click or double-click Mail.
To locate the Mail item, open Control Panel, and then in the Search box at the top of window, type Mail. In Control Panel for Windows XP, type Mail in the Address box.
Click Show Profiles.
Type a name for the profile, and then click OK.
Select Manual setupor additional server types, and then click Next.
Select POP or IMAP, and then click Next.
Enter your name and email address, and then select POP3 for the Account Type.
Enter your Incoming mail server and Outgoing mail server (SMTP) details, enter your logon information, and then click Next.
Note Go to your email server host's website or contact them to collect the incoming and outgoing mail server details.
Your account settings will be tested to verify that they are correct:
If the tests are completed successfully, click Close.
If you receive an error during the tests, click Close. Correct the information in the account settings, and then repeat steps 9 and 10 until the account settings are correct.
In Mail, make sure that the Always use this profile option is selected, and then select your new profile name from the list.
Method 3: Use Outlook 2013
If possible, use Outlook 2013 instead of Outlook 2016 to connect to your IMAP account. This issue does not occur in Outlook 2013.
Microsoft is researching this problem and will post more information in this article when the information becomes available.