As an Office 365 administrator, you can apply your company branding to customize the look of your organization’s Office 365 Message Encryption email messages as well as the contents of the encryption portal. You can customize the following aspects of the viewing experience for recipients of encrypted email messages:

• Introductory text of the email that contains the encrypted message
• Disclaimer text of the email that contains the encrypted message
• Text that appears in the OME portal
• Logo that appears in the email message and OME portal
• Background color in the email message and OME portal

You can also revert back to the default look and feel at any time.

Below is the default message your recipient will see when they receive an encrypted email message.

Customize the Message

To customize the OME message you will first need to connect to Exchange Online using Remote PowerShell. You then want to get your OME template identity which is most likely, “OME Configuration”. To get the template identity run:

Get-OMEConfiguration

 

Now that we know our template that we will be working with, we can start customizing it to fit our needs.

It is important to note that when you make changes to your OME Template, it will clear prior changes. In my example below I use the Set-OMEConfiguration cmdlet to add EmailText to my template and then confirm it works. When I next use the Set-OMEConfiguration cmdlet to add DisclaimerText, I notice that the EmailText is now Null. So if you want to make multiple changes to your template, make sure you pass it all in one command.

E-Mail Text

The E-mail text will sit below the “Read the message” button on the encrypted e-mail. In my example I am going to set my email text to “TEST EMAIL TEXT”. You text can be up to 1024 characters in length.

Set-OMEConfiguration -Identity "OME Configuration" -EmailText "TEST EMAIL TEXT"

Now when I send another encrypted message, my recipient will see the email text.

Disclaimer

The DisclaimerText parameter specifies the disclaimer text in the email that contains the encrypted message. The maximum length is 1024 characters.

Set-OMEConfiguration -Identity "OME Configuration" -DisclaimerText "THIS IS THE DISCLAIMER TEXT! OPEN AT YOUR OWN RISK.."

Portal Text

The PortalText parameter specifies the text that appears at the top of the encrypted mail viewing portal. The maximum length is 128 characters. This is seen when you user authenticates and views the encrypted message.

Set-OMEConfiguration -Identity "OME Configuration" -PortalText "OME PORTAL TEXT"

Image

The Image parameter identifies and uploads an image that will be displayed in the email message and in the Office 365 portal.

You need to read the file to a byte-encoded object using the Get-Content cmdlet, for example, -Image (Get-Content “C:\Temp\OME Logo.gif” -Encoding byte)

• Supported file formats: .png, .jpg, .bmp, or .tiff
• Optimal size of logo file: less than 40 KB
• Optimal dimensions of logo image: 170×70 pixels

Set-OMEConfiguration -Identity "OME configuration" -Image (Get-Content "C:\Automation\logo.png" -Encoding byte)

And yes you can make the logo a transparent image

Background Color

The BackgroundColor parameter specifies the background color. Valid values are:

• An available text value (for example, yellow is 0x00FFFF00).
• $null (blank). This is the default value.

For the list of available hex and text values, see Background colors for Office 365 Message Encryption (https://support.office.com/article/1508cb35-c5ff-4523-b579-947b21d5515f).

Set-OMEConfiguration -Identity "OME Configuration" -BackgroundColor green

Introduction Text

The default introduction text is “has sent you a protected message.” In my example below I changed it to “”has sent you super secret stuff! Don’t tell nobody” ”

Set-OMEConfiguration -Identity "OME Configuration" -IntroductionText "has sent you super secret stuff! Don't tell nobody"

Read Button Text

The ReadButtonText is straight forward. It changes the text on the Read button which normally is “Read the message”. In my example I will change it to “Hurry!”.

Set-OMEConfiguration -Identity "OME Configuration" -ReadButtonText "HURRY!"

 

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Sources

https://docs.microsoft.com/en-us/office365/securitycompliance/add-your-organization-brand-to-encrypted-messages 

https://docs.microsoft.com/en-us/powershell/module/exchange/encryption-and-certificates/set-omeconfiguration?view=exchange-ps