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Management often demands branding uniformity across all systems, including email signatures. In addition, IT has to ensure that all emails leave the company network with a common disclaimer. Exchange transport rules (also known as mail flow rules) can take actions on emails before delivery. You can use them to reject messages based on content, send messages to moderators, and add signatures and disclaimers.
We will use HTML with the transport rule “Append the disclaimer…” to construct a standardized signature that uses Active Directory attributes to populate the signature. We’ll use an exception to prevent the email signature from appending repeatedly to the bottom of the same email chain. Last, we’ll look at some strategies for enforcing signature policies and preventing users from adding their own signatures.
Set up transport rule to add disclaimer ^
Start by signing into to the Office 365 Exchange Admin center (Admin center preview home -> Admin centers -> Exchange.) Next, click on mail flow -> rules. Create a new rule by clicking on the + button and choose Apply disclaimers….
Name the rule something like “HTML Signature 1,” and apply a condition that says to use the rule if “The sender … is this person,” and send it to yourself or a test account to work out any bugs.
Next, click Enter text… and copy your signature HTML code into the text box. Below is a sample signature that uses variable values from Active Directory and applies them to the different fields. You can use any of the following variables, placing them between two sets of double percentage symbols.
UserLogonName, DisplayName, FirstName, Initials, LastName, PhoneNumber, OtherPhoneNumber, HomePhoneNumber, OtherHomePhoneNumber, PagerNumber, MobileNumber, FaxNumber, OtherFaxNumber, Email, Street, POBox, City, State, ZipCode, Country, Title, Department, Manager, Office, Company, Notes, CustomAttribute1 – CustomAttribute15
Sample signature and disclaimer ^
-- <br> <img alt="Contoso Corp" src="https://samples.file.core.windows.net/blob1/ContosoCorp_ESig.png"><br> <b>%%DisplayName%%</b><br> %%Title%%<br> %%PhoneNumber%%<br> <div> <p style="font-size:8pt; line-height:10pt; font-family: 'Arial','Arial',serif;">This message contains confidential information and is intended only for the individual(s) addressed in the message. If you are not the named addressee, you should not disseminate, distribute, or copy this email. If you are not the intended recipient, you are notified that disclosing, distributing, or copying this email is strictly prohibited. </p> </div> </br>
I recommend that you size your logo image first, then upload, and make your file publicly accessible in Azure with the Azure Storage Explorer. If you do not already have the Azure Storage Explorer utility, you can find it here. MS SQL Express and the Microsoft Azure Storage Emulator are prerequisites for the Azure Storage Explorer utility.
Preventing stacks of signatures ^
You may have noticed that I included two dashes and a space, followed by a break at the top of my signature. This signature delimiter helps mail clients know that a signature will begin; the receiver can choose to remove the sig block as desired.
Next, modify the fall back if the disclaimer can't be inserted setting to the Ignore action by clicking Select one....
I recommend adding an action to remove the signature if the text that matches your signature already exists. As stated earlier, if you do not add this exception, you’ll end up with stacks of signatures at the bottom of an email chain—more on this later.
To prevent the transport rule disclaimer/signature from being appended repeatedly each time a messages is sent, click on More options…, then the add exception button, and then select Except if… The subject or body includes… any of these words. Next copy a snippet of text from your disclaimer and enter it into the text box and click the + button. Your final rule should look similar to the following screenshot. Be sure to test extensively by sending email from different clients and confirming the signature behavior when you reply and forward messages.
One caveat: You cannot add multiple signatures, such as a separate signature for each reply or forward, to the same email chain with a transport rule. However, you can use one of several third-party tools to modify this behavior, if desired.
Prevent users from adding their own signatures ^
Without realizing it, users who create their own personalized signatures in their mail clients could produce duplicate signatures at the bottom of their messages. To prevent this from happening in Outlook Webmail, you can go into the Office 365 Admin Center -> Exchange Admin Center -> Permissions -> Outlook Web App policies -> Features, and then uncheck Email Signature.
To prevent users from creating signatures in Outlook, you can use the Group Policy Do not allow signatures for email messages that Microsoft provides with the ADMX templates for Office. This guide describes how to add the templates and deploy the policy. Alternatively, you can follow this guide to disable the ability to create a signature in Outlook by using a group policy object (GPO) that modifies the registry.
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In the event your organization wants a standardized signature, with a little work you can create a transport rule in Office 365 to append a disclaimer containing a signature to all outbound email. The disclaimer will include a personalized HTML signature and logo by pulling its data from Active Directory and Azure Storage. To prevent multiple signatures from appearing in the same email chain, you may want to disable the end user’s ability to create his or her own signature with a GPO, an Outlook Webmail Policy, and an exception within your transport rule.