"Bad Command. 12" error occurs and IMAP CAPABILITY commands are not offered in an Exchange Server 2013 environment

Symptoms

Consider the following scenario:

• You deploy Microsoft Exchange Server 2013 and Microsoft Exchange Server 2010 in a co-existence environment.

• All mailboxes are located in Exchange Server 2010.

• You point all DNS records to Microsoft Exchange 2013 Client Access server for the client connection.

In this scenario, when Internet Message Access Protocol (IMAP) client sends CAPABILITY commands for ID and MOVE that can be used in Exchange Server 2013, Exchange Server 2010 cannot respond to these commands. Additionally, the following error message is thrown:

Cause

This issue occurs because Exchange Server 2010 does not support IMAP capability for ID and MOVE commands that are supported in Exchange Server 2013.

Resolution

To resolve this issue, install Cumulative Update 9 for Exchange Server 2013, and

create a setting override as follows:

New-SettingOverride <override name> -Component Imap -Section RfcIDImapCafe -Reason “Disable ID command in Cafe” –Parameters @(“Enabled=false”)

Once all mailboxes have been moved to Exchange Server 2013 or Exchange Server 2016, the setting override can be removed by using the Remove-SettingOverride commandlet.

Workaround

To work around this issue, manually point back the DNS records to Exchange 2010 Client Access servers for client connection.

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about how to disable IMAP commands in Cafe after you install Cumulative Update 9, run the following PowerShell cmdlet:

New-SettingOverride <override name> -Component Imap -Section RfcIDImapCafe -Reason “Disable ID command in Cafe” –Parameters @(“Enabled=false”)If you want to re-enable the ID command, you have to remove the previous setting override by running the Remove-SettingOverride <override name> cmdlet.

Note

• For the <override name> parameter, you can use any name, such as "DisableID". Similarly, you can specify your own reason for the –Reason parameter.

• You may also want to disable the MOVE command just to be safe. To do that, run another New-SettingsOverride command by using different override name and replace the value of the Section parameter as RfcMoveImapCafe.

• When you run the command, it should become effective within 15 minutes.