https://technet.microsoft.com/en-us/library/dn879084(v=exchg.150).aspx

Direct link to Performance Counters

https://technet.microsoft.com/en-us/library/dn904093(v=exchg.150).aspx

Clean-MailboxDatabase command has  been decommissioned for Exchange 2013 and replaced with Update-StoreMailboxState http://technet.microsoft.com/en-us/library/jj860462(v=exchg.150).aspx

Update-StoreMailboxState require the GUID of a mailbox to execute so it usually easier to run in combination with Get-MailboxStatistics like the example below

Get-MailboxStatistics -Database MDB02 | ForEach { Update-StoreMailboxState -Database $_.Database -Identity $_.MailboxGuid -Confirm:$false }

Use the Update-StoreMailboxState cmdlet to synchronize the mailbox state for a mailbox in the Exchange mailbox store with the state of the corresponding Active Directory user account. This is especially useful when you want to show disconnected mailboxes or reflect a change in mailbox quota settings

The Windows Azure Active Directory Sync tool (DirSync) is used to provision user accounts from Windows Active Directory on-premises to Azure Active Directory in the cloud. DirSync will synchronize changes to user accounts made on-premises to the cloud so that cloud users have access to directory information and can sign-in. This document describes how to backup and later restore the database and encryption keys required for a DirSync install. This will reduce the time to resynchronize user accounts from your on-premises Active Directory to Windows Azure Active Directory when there has been a failure of the previous DirSync installation.

Great document http://www.microsoft.com/en-us/download/details.aspx?id=42524

Exchange 2013 CU6 databases unexpectedly fail over in a co-existence environment with Exchange 2007: This is an issue that has come up after the release of Exchange 2013 CU6. The details of this issue are available in KB:2997209 – “Exchange Server 2013 databases unexpectedly fail over in a co-existence environment with Exchange Server 2007”
A fix is available for this issue from Microsoft Support.

You cannot route ActiveSync traffic to Exchange 2007 mailboxes after you upgrade to Exchange 2013 CU6: The details of this issue are available in KB:2997847 – “You cannot route ActiveSync traffic to Exchange 2007 mailboxes after you upgrade to Exchange 2013 CU6”.
 A fix is available for this issue from Microsoft Support.

Exchange Online mailboxes cannot be managed by using EAC (Exchange Administration Center) after you deploy Exchange 2013 CU6: This is another issue that has come up after the release of Exchange 2013 CU6. The details of this issue are available in KB:2997355 – “Exchange Online mailboxes cannot be managed by using EAC after you deploy Exchange Server 2013 CU6”
A script is available for this issue from Microsoft Support.
Please be advised if you installed Exchange in an alternate location (other than the default) then you would need to modify the directory path in the script.

The Exchange team announced Exchange Server 2013 Cumulative Update 6. CU6 represents the continuation of our Exchange 2013 servicing and builds upon Exchange 2013 CU5. A complete list of customer reported issues resolved in Exchange 2013 CU6 can be found in KB 2961810. Customers running any previous release of Exchange 2013 can move directly to CU6 today. Customers deploying Exchange 2013 for the first time may skip previous releases and start their deployment with CU6 as well. CU6 includes Exchange-related updates to Active Directory schema and configuration.

The Exchange team announced today the availability of Update Rollup 7 for Exchange Server 2010 Service Pack 3. A complete list of issues resolved in Exchange Server 2010 Service Pack 3 Update Rollup 7 may be found in KB2961522.

The Exchange team announced today the availability of Update Rollup 14 for Exchange Server 2007 Service Pack 3. More information on this rollup is available in KB2936861.