Can't uninstall Exchange 2007 SP1 Mailbox role from Server 2008 R2

If you are getting error:
"An error occurred. The error code was 3221685466. The message was The service is already registered.."
while trying to uninstall Exchange 2007 SP1 Mailbox role from Server 2008 R2 (RC in my case)
try changing registry key value from "Uninstall" to "Install" located at
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\v8.0\Mailbox\
after that try uninstalling again.

Error when trying to Export-Mailbox to .pst file (or import-mailbox) on Exchange Server 2007 SP1

When trying to export mailbox to .pst file in Exchange Server 2007 SP1 using Exchange Management Shell command "Export-Mailbox" I have encountered an error:
"Failed to copy messages to the destination mailbox store with error: MAPI or an unspecified service provider. ID no: 00000000-0000-00000000.."

To solve this run this command in Exchange Management Shell
"Get-Mailbox Add-MailboxPermission -User "" -AccessRights FullAccess"
and try exporting again.

Removing last Exchange 2007 server from your organization

Had to uninstall exchange serve from SBS 2008, as it was the last Exchange server in organization I encountered number of problems trying to uninstall it.

One of those problems are that you cannot uninstall Exchange server while it contains Public Folder Replicas and you can't move them to another server because there is none.

Browsing the web I was finally able to solve this problem, for full artcile just follow the link and read the comments.
Here's summary:

1. You'll have to keep at least one mailbox with administrator rights.
2. Open Power-Shell and enter the following commands:

Get-PublicFolder -Server "\" -Recurse -ResultSize:Unlimited | Remove-PublicFolder -Server -Recurse -ErrorAction:SilentlyContinue

Get-PublicFolder -Server "\Non_Ipm_Subtree" -Recurse -ResultSize:Unlimited | Remove-PublicFolder -Server -Recurse -ErrorAction:SilentlyContinue

3. Remove all mailboxes on your server.
4. Remove Exchange 2007 server from "Programs and Features" in control panel.

Links:
http://blogs.technet.com/asiasupp/archive/2007/06/26/public-folder-replicas-prevent-uninstall-exchange-2007.aspx

OWA login requires "domain\username". How to login wit "username" only?

When logging on to my exchange 2007 server OWA, I need to enter "domain\username", I want to be able to log in by using "username" alone.
So here is how I did that:
Open Exchange Management Console, expand Server Configuration and find Outlook Web Access tab in Client Access. Double click "OWA (Default Web Site)" and go to Authentication tab. Uncheck "Integrated Windows authentication" box (screenshot) and click OK.
Open your webmail and try to log in without specifying a "domain\" in your User Name.

Activesync error 0x85010001

User was getting this error code on his mobile device when trying to synchronize.
Temporary solution achieved by disabling Windows Authentication (screenshot) for Microsoft-Server-ActiveSync in IIS Manager.

Users unable to send mail via outlook (550 5.7.1 Client does not have permissions to send as this sender)

Had this problem on my exchange 2007 server (hub transport role) for a long time.
Some users could receive mail, but when trying to send using POP3 or IMAP outlook account they got '550 5.7.1 Client does not have permissions to send as this sender' error. They could send and receive emails fine when logged into OWA.
This problem seems to have something with SMTP authentication, the workaround I was using was letting those users to open relay on my server, but recently my server started sending spam so I was forced to look for solution to this problem once again (I've tried to resolve this problem before, but unsuccessfully).

I had configured send connector, also receive connector, but nothing seemed to work. Today browsing the web for answer I think I finally got it to work.

Following information found on the web I've opened Exchange Management Shell and ran this cmdlet:
get-receiveconnector "receive_connector_name" | add-adpermission -user AU -extendedrights ms-Exch-SMTP-Accept-Authoritative-Domain-Sender

Tried to send email again and it disappeared from the outbox.

Links:
http://www.exchangeninjas.com/TUPMServerResponses
http://forums.msexchange.org/m_1800412481/printable.htm