Scenario

Transport Neutral Encapsulation Format (TNEF) is a proprietary format created by Microsoft to enable some Outlook-specific features. Other mail clients may not support TNEF, which may cause compatibility or display issues when configured incorrectly.

This article provides a resolution to scenarios where tasks are missing from an email when a signature is applied, voting buttons are missing from an email when a signature is applied, or contacts are missing from an email when a signature is applied.

Reason

Tasks, voting buttons and contacts are stored as MAPI properties; when these are used, the message will be encapsulated in a Transport Neutral Encapsulation Format (TNEF). When the message is sent to Exclaimer via the M365 connector, the message is converted by Exchange from MAPI to MIME, which strips out MAPI properties.

Resolution 

To resolve this, you need to create an internal remote domain and set TNEF to True on that domain:

You can do this either by:

• PowerShell 
• Exchange admin center

To create and enable TNEF for internal domains only using PowerShell commands:

1. Connect to Exchange Online Powershell.
   
   To do this:
   
   - Open the Windows PowerShell and run this command as an Administrator:
   
   Install-Module -Name ExchangeOnlineManagement
   
   - Confirm that you want to install this PowerShell module.
   NOTE: For additional installation options, see ExchangeOnlineManagement.
   
   
2. Run this command:
   
   New-RemoteDomain -DomainName "domain.com" -Name <DisplayName>
   - where DomainName must be the domain you are sending from. The name can be whatever you wish - we recommend 'internal'.
   
   
3. Run this command:
   
   Set-RemoteDomain -Identity "DisplayName" -TNEFenabled $true

To create and enable TNEF for internal domains only using the Exchange admin center:

1. Navigate to https://admin.exchange.microsoft.com/#/remotedomains
   
   
2. Sign in with your global administrator credentials.
   
   
3. Click Add a remote domain.
   
   
   
   A New remote domain screen is displayed.
   
   
4. In Name, enter a domain name. In this example, we have entered 'Internal'.
   
   
5. In Remote domain, enter your internal domain name. In this example, we have entered 'Internaldomain.com'.
   Example:
   
   
   
6. Click Next to proceed.
   
   
7. In Out of Office automatic reply types, select Allow only external out of office replies. 
   
   
8. In Automatic replies, select Allow automatic replies and Allow automatic forwarding.
   
   
   
   
9. Click Next to proceed.
   
   
10. In Message reporting, select Allow delivery reports and Allow non-delivery reports.
    
    
    
    
11. Click Next to proceed.
    
    
12. In Use rich-text format, select Always.
    
    
13. From the MIME character set drop-down, select Unicode (UTF -8).
    
    
14. From the Non-MIME character set drop-down, select Unicode (UTF -8).
    
    
    
    
15. Click Next to proceed.
    
    
16. Now, review the settings you've selected.
    
    
    
    
17. Click Save to save the settings. 
    
    A message is displayed that the new remote domain has been successfully created.