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Windows 7: Outlook 2007, Exchange 2007, S/MIME and Winmail.dat

25 Nov 2009   #1

Windows 7 Ultimate x64
Outlook 2007, Exchange 2007, S/MIME and Winmail.dat

Ok so this probs isn't the ideal forum for Outlook and Exchange queries, but I know theres many skilled technical people on here, so posting on the off chance.

Anyway I run Outlook 2007 at work and I recently migrated from Exchange 2003 to Exchange 2007.
I like to secure my email communication as much as possible and thus like to make use of the free Digital Signature obtainable from Comodo.

Now my problem is when I send an email signed with my digital signature, a winmail.dat file is attached to the message. I have a few recipients that have their mail servers configured to block *.dat file attachments.

Reading resources on the web it seems the winmail.dat file is attached to RTF encoded messages.
However the winmail.dat file is attached even when sending the message in plain text when also signing the message with my digital signature.
I know I can just decide not to sign the message to problem recipients, but I never had this issue with Exchange 2003 so don't see why I should have to use this workaround.

Wake up Microsoft, not everyone in the world is running Exchange server and Outlook clients!!!

Hopefully some email expert will come across this, if not thanks for looking.


My System SpecsSystem Spec
15 Jan 2010   #2

Windows 7 Ultimate

I have exactly same problem with Outlook 2007 without any Exchange server. Is there any solution for this?

My System SpecsSystem Spec
24 Sep 2010   #3

win xp 32 Bit
Outlook 2007 Exchange 2007 und winmail.dat


my solution was:
I created a contact to where i wanted to send encrypted email and attached a certificate using cerutil.exe.
Now in that contact there is an option "Use MAPI Rich Text format" which is normaly set to "default". If you set that to never it' will work

regards, Heinz
My System SpecsSystem Spec

24 Sep 2010   #4

Win7 HP (x64)/Win7 Ultimate (x64)


Not sure if it will but hope this helps in some way - check the last three paragraphs :)


To control whether or not to send messages in RTF, follow the option that best meets your situation:
  • Creating Custom Recipients
    When an administrator creates a custom recipient using the Microsoft Exchange Administrator program, click to clear the Always Send To This Recipient In Microsoft Exchange Rich-Text Format check box.
  • Modifying Existing Microsoft Exchange and Custom Recipients
    An administrator can prevent an existing user account (Microsoft Exchange user or custom recipient) from sending RTF information by clicking to clear the MAPI Recipient check box on the Advanced property page of the recipient's properties. An administrator can view the recipient's properties by clicking the recipient name, and then clicking Properties on the File menu.
  • Addresses in the Personal Address Book
    End users can modify the Internet addresses in a personal address book (PAB) to prevent sending RTF information by clicking to clear the Always Send To This Recipient In Microsoft Exchange Rich-Text Format check box in the SMTP - Address property page of the Internet address in the PAB. To obtain the properties of an entry in the PAB, click the entry, and then on the File menu, click Properties.
  • Configuring the Internet Mail Connector (IMC)
    An administrator can configure the IMC with RTF options in the following manner:
    1. Open the Internet Mail Connector Properties page.
    2. Click the General tab.

      The Send Microsoft Exchange Rich Text list box controls the sending of rich-text data. There are three values to choose from:
      • If the value is set to User, the recipient properties are used to determine whether or not to send RTF information.
      • If the value is set to Always, RTF information is always sent, regardless of the recipient properties.
      • If the value is set to Never, RTF information is never sent.
      An administrator can also configure the option to send RTF information on a domain-by-domain basis. To define e-mail domains and the message settings for that domain, click the E-Mail Domain button of the Internet Mail tab.
  • One-Off Addressing
    Anyone can send e-mail to an Internet user from an Exchange or Outlook client by using one-off addressing. One-off addressing allows you to send a message to addresses that are not in the PAB, the global address list, or in any recipient containers.

    Depending on the type of the one-off address used, RTF information is or is not sent with the message:
    • Rich-Text Information Is Sent:

      If the one-off address has the following format, RTF information is sent with the message:

      [SMTP:SMTP Address]

      where SMTP Address is any valid SMTP address, for example:

      To verify that RTF information is sent:
      1. In a new message, type the address in the SMTP address format in the To field. On the Tools menu, click Check Names. You will see the SMTP address without the "SMTP:" and the name is underlined.
      2. Double-click the address to bring up its properties.

        If the Always send to this recipient in Microsoft Exchange rich-text format check box is selected, rich-text information (the Winmail.dat file) is sent along with the message.
    • Rich-Text Information Is Not Sent:

      If an end user is using a one-off address and does not want to send RTF information to the recipient, the address should have the following format:

      SMTP Address

      where SMTP Address is any valid SMTP address, for example:

      NOTE: Unlike the address in the "Rich-Text Information Is Sent" section, the SMTP address is not proceeded by "SMTP:" and the address is not enclosed in square brackets ([]).

      If the Check Names check box is selected, the properties of the address will show that the rich-text option is not selected.

      However, no matter what option is selected for the address of the recipient, the IMC settings determine whether or not RTF information is transmitted. If the IMC is set to never send RTF information, even if the properties of the recipient address have the rich-text option selected, no RTF information is transmitted.

      If the IMC has separate settings for individual domains, the settings for those domains takes precedence for all messages addressed to users in those domains.

      Optionally, instead of typing the hex value in the edit field, click Editor, select File Version, and then click OK. On the File Version tab, in the fields provided, type the appropriate build number of Imcadmin.dll in the following format 5.5.2650.24. To determine the correct build number of Imcadmin.dll, do a search for the file on the Exchange Server. Once you have found it, right-click it, click Properties, and then click the Version tab. The build number appropriate to your server is listed here. Type this number into the value field and click OK. You then see the appropriate Hex value in the edit field.
My System SpecsSystem Spec

 Outlook 2007, Exchange 2007, S/MIME and Winmail.dat

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