To avoid releasing potentially private information on outgoing email messages, categories are not sent with email in Outlook when you use Exchange server mailboxes. When you use categories with internal codes or potentially embarrassing keywords, the recipient will not see them.

This does not apply to POP3 or IMAP accounts. The Category is removed by Exchange Server's transport rules, not Outlook, when the message is sent. A rule in Outlook 2007 and 2010 removes categories as messages are downloaded; Outlook 2013 and up does not have this rule, users will need to create the rule to remove categories.

If you need to send categories on outgoing email you can use the SendPersonalCategories registry entry.

Warning: when making this change, the categories will be included on the sent message and the recipient will be able to see the category (unless the recipient uses a rule to remove categories from messages they receive).

Create the key or path if it does not exist. This key should take effect without restarting Outlook.
 

User keys

Outlook 2016

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences
DWORD: SendPersonalCategories
Value Data: 1 to keep categories on sent mail, 0 to not include categories

Outlook 2013

HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Preferences
DWORD: SendPersonalCategories
Value Data: 1 to keep categories on sent mail, 0 to not include categories

HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Preferences
DWORD: SendPersonalCategories
Value Data: 1 to keep categories on sent mail, 0 to not include categories

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Preferences
DWORD: SendPersonalCategories
Value Data: 1 to keep categories on sent mail, 0 to not include categories

If you setting the SendPersonalCategories value, users can still delete the categories as messages arrive by using a rule.

Do it for me

If you don't want to edit the registry yourself, you can download and run a registry file to make the changes. This reg file also sets AcceptCategories value.

Outlook 2016Outlook 2013Outlook 2010
Outlook 2007

Policy keys

Policy keys are generally used by administrators, usually in a GPO. In the past, home users could use policy keys too, however many policy keys won't work in the consumer versions of Outlook 2013 and Outlook 2016.
Outlook 2016

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\Preferences
DWORD: SendPersonalCategories
Value Data: 1 to keep categories on sent mail, 0 to not include categories

Outlook 2013

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Outlook\Preferences
DWORD: SendPersonalCategories
Value Data: 1 to keep categories on sent mail, 0 to not include categories

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\Preferences
DWORD: SendPersonalCategories
Value Data: 1 to keep categories on sent mail, 0 to not include categories

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\Preferences
DWORD: SendPersonalCategories
Value Data: 1 to keep categories on sent mail, 0 to not include categories

If you setting the SendPersonalCategories value, users can still delete the categories as messages arrive by using a rule.

Do it for me

If you don't want to edit the registry yourself, you can download and run a registry file to make the changes. This reg file also sets AcceptCategories value.

Outlook 2016Outlook 2013Outlook 2010
Outlook 2007

Default Rule to Remove Categories

Outlook 2007 and up have a default rule that removes categories from messages as they arrive. Delete the rule or disable it if you want to keep the categories.

Remove Categories using a Macro

If categories are being sent, you can use a macro to remove the categories as the message is sent. Place the macro into ThisOutlookSession.

Private Sub Application_ItemSend(ByVal Item As Object, Cancel As Boolean)
Item.Categories = ""
Item.Save
End Sub

Exchange rule to remove categories

In Exchange 2007 and up, categories are removed from messages. To disable it, the administrator can use this cmdlet to change the transport setting.

Set-transportconfig -clearcategories $false

Other methods

If you need to include the category on a one time basis, drag the item to the hard drive, zip it and email the zip file. The recipient will drag the item to a folder in their Outlook and if using Outlook 2007, can add the categories to their master list by using the Upgrade to color categories option in the root folder properties.

Add Categories to Master list

In Outlook 2007 or 2010, to add a category that is not in your master list, to your master list, select it (so its highlighted) and click the New button.

Outlook will assign the next unused color - change the color and set a shortcut key, if desired, then click Save.

Adding Categories when Composing Email

The Categories button is not available when you are composing new messages. When you need to assign categories, you need to add the category to the message either in the Sent folder or in the Outbox.

To add the category before hitting Send, you can use VBA to open the Categories dialog. Add the following code to the VB Editor and then add a button to the QAT, Ribbon, or Toolbar of a message form. Click the button to open the Category dialog.

'by Michael Bauer
'//www.vboffice.net/en/developers/assign-email-categories-before-sending
Public Sub ShowCategoriesDialog()
  Dim Mail As Object
  Set Mail = Application.ActiveInspector.CurrentItem
  Mail.ShowCategoriesDialog
End Sub