This problem just started happening a few days ago. I have a few users that connect to the Exchange 2010 server via IMAP.
They reported to me that they kept getting messages that they were unable to connect. I had just updated the SSL Certificate on the server so I thought I would go look at the settings for IMAP in the EMC / Server Configuration / Client Access / IMAP4. Being that the authentication was set to using TLS. Made sure the certificate name was correct. This all looked correct. I verified that all users had rights to access the IMAP in AD. All of this appears to be correct.
So I thought well lets remove the TLS and set it to plain text logon and basic authentication. Then made changes to the client machine I was testing this with (outlook client). On the "Log onto incoming mail server (IMAP)" I get failed with the message, "Log onto incoming mail server (IMAP): General authentication failed. None of the authentication methods supported by your IMAP server (if any) are supported on this computer." I then thought well lets try POP3 and both with and with out encryption I get the same results.
Once again the only thing that has changed is new SSL cert for OWA. Which by chance works fine as well as ActiveSync. All users are getting email via their cell phones and standard exchange connectors for Outlook are working just fine.
Thanks for any help in advance.
Also sorry I put this under Exchange 2013 but there was no Exchange 2010 in the drop down for forums.