You can specify whether Transport Neutral Encapsulation Format (TNEF) should be preserved or removed from messages that leave the Exchange organization. TNEF, also known as Outlook Rich Text Format, is a Microsoft-specific format for encapsulating MAPI message properties. All versions of Microsoft Outlook fully understand TNEF. However, email clients that don't understand TNEF typically display TNEF formatted messages as plain text messages with Winmail.dat or Win.dat attachments.

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TNEF conversion options for remote domains

TNEF conversion options for mail users and mail contacts

TNEF conversion options in Outlook

Order of precedence for TNEF conversion options

When you configure TNEF conversion options for a remote domain, those TNEF conversion options are applied to all messages sent to that domain. You use the TnefEnabled parameter on the Set-RemoteDomain cmdlet to configure the TNEF conversion options for a remote domain. For more information about remote domains, see Remote Domains.

For remote domains in your organization, you have the following configuration options for TNEF conversion:

• TNEF enabled   TNEF is used for all messages sent to the remote domain. The corresponding value for the TnefEnabled parameter is $true.
  
  
• TNEF disabled   TNEF is never used for any messages sent to the remote domain. The corresponding value for the TnefEnabled parameter is $false.
  
  
• Unspecified   TNEF messages aren't specifically allowed or prevented for recipients in the remote domain. Whether TNEF messages are sent to recipients in the remote domain depends on the specific setting on the mail contact or mail user, or the setting specified by the sender in Outlook. The corresponding value for the TnefEnabled parameter is $null (blank). This is the default setting.
  
  

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When you configure TNEF conversion options for a mail contact or a mail user, those TNEF conversion options are applied to all messages sent to that specific recipient. You use the UseMapiRichTextFormat parameter on the Set-MailUser and Set-MailContact cmdlets to configure the TNEF conversion options for mail users and mail contacts.

For mail users and mail contacts in your organization, you have the following configuration options for TNEF conversion:

• Always   TNEF is used for all messages sent to the recipient. The corresponding value for the UseMapiRichTextFormat parameter is Always.
  
  
• Never   TNEF is never used for any messages sent to the recipient. The corresponding value for the UseMapiRichTextFormat parameter is Never.
  
  
• Use default settings   TNEF messages aren't specifically allowed or prevented for the mail user or mail contact. Whether TNEF messages are sent to the recipient depends on the specific setting for the corresponding remote domain or the setting specified by the sender in Outlook. The corresponding value for the UseMapiRichTextFormat parameter is UseDefaultSettings. This is the default setting.
  
  

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Senders can control the default TNEF message conversion options for TNEF messages sent to all recipients outside the Exchange organization. These options are called Internet message format options. The options only apply to remote recipients, and not to recipients in the Exchange organization.

Note:
The following options define how messages containing Outlook rich text are handled when sent to external recipients. If the message format you're using is HTML or plain text, these settings don’t apply.

You have the following TNEF conversion options in Outlook:

• Convert to HTML format   This is the default option. Any TNEF messages sent to remote recipients are converted to HTML. Any formatting in the message should closely resemble the original message. MIME-encoded HTML messages are supported by many, but not all, email clients.
  
  
• Convert to Plain Text format   Any TNEF messages sent to remote recipients are converted to plain text. Any formatting in the message is lost.
  
  
• Send using Outlook Rich Text Format   Any TNEF messages sent to remote recipients remain TNEF messages.
  
  

You can configure these options in the following locations in Outlook:

• Outlook 2010 or Outlook 2013   File > Options > Mail > Message format.
  
  
• Outlook 2007   Tools > Options > Mail Format > Internet Format.
  
  

Senders can also control the default TNEF message conversion options for TNEF messages sent to specific recipients outside the Exchange organization. These options are called Internet recipient message format options. The options only apply to remote recipients stored in your Contacts folder, and not to recipients in the Exchange organization. You have the following TNEF conversion options for remote recipients in your Contacts folder:

• Let Outlook decide the best sending format   This is the default setting. This setting forces Outlook to use the TNEF conversion option that's specified by the default Internet format. The possible values are Convert to HTML format, Convert to Plain Text format, or Send using Outlook Rich Text Format. Therefore, the TNEF message may be left as TNEF, converted to HTML, or converted to plain text. If you want to make sure that the TNEF message remains TNEF for this recipient, you should change this setting from Let Outlook decide the best sending format to Send using Outlook Rich Text format.
  
  
• Send Plain Text only   Any TNEF messages sent to the recipient are converted to plain text. Any formatting in the message is lost.
  
  
• Send using Outlook Rich Text format   Any TNEF messages sent to remote recipients remain TNEF messages.
  
  

You can configure these options for a contact in the following locations in Outlook:

• Outlook 2010 or Outlook 2013   Open the contact card, double-click the email address, click the View more options for interacting with this person icon, and select Outlook properties. In the E-mail Properties dialog box, select Internet format.
  
  
• Outlook 2007   Open the contact card, double-click the E-mail field and select Internet format.
  
  

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Exchange uses the order of precedence as described in the following list to determine the TNEF conversion options for outgoing messages sent to recipients outside the Exchange organization:

1. Outlook settings
   
   
2. Mail user or mail contact settings
   
   
3. Remote domain settings
   
   

The list specifies the order of precedence from lowest to highest. A setting made at a higher level overrides a setting made at a lower level.

Exchange never sends Summary Transport Neutral Encoding Format (STNEF) messages to external recipients. Only TNEF messages can be sent to recipients outside the Exchange organization.

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