recipient can't open .dat attachment

1st time user… sent an encrypted mail. User recieves mail and an attachment of type xxx.dat

What next… how does he open the mail?

Hi, bohica910
It seems to be that recipient uses Web interface to receive a mail (he checks and reads e-mails via browser, not via e-mail client)… So he needs to download e-mail via e-mail client like Outlook Express/2003/2007/Windows Live Mail/ etc. (which support S/MIME settings). Also, user should have his own certificate to successfully decrypt incoming encrypted e-mail.

if it doesn’t help you,give more details, please:

  • Your CSE version
  • Your CSE options (Start->All programs->Comodo->SecureEmail->SecureEmail Configuration->Security)
  • Your e-mail client
  • Does recipient try to view e-mail via web interface (using browser) or via mail client ?
  • Does recipient has his own certificate ?


Hi Bohica910.

It seems to me that you have sent e-mail encrypted with the session certificate. To read this e-mail your recipient should use instructions in the e-mail body. For the case if it is unreadable for any reasons I’m providing this info here:

To read it, please choose one of the following options: ( there is no charge for either option )

Download and Install Comodo SecureEmail software

If you are using just about any e-mail software package for Microsoft Windows and are likely to be receiving more secure e-mail messages from SENDER_EMAIL_ADDRESS or other senders, you should download and install your own version of Comodo SecureEmail. Click here for more information or to download the software.

Read the message online using the Comodo Web Reader service

If you are using web-based e-mail or a non-Windows operating system for e-mail, you can view your message on a secure website designed expressly for this purpose. Simply forward this e-mail to secure-read[at] and you will receive a return e-mail that provides access to that website.</blockquote>

When You install CSE on the Recipient PC you will be able to read all e-mails encrypted with the session certificates as normal encrypted one’s and CSE will automatically update your correspondents with the latest valid public key of your certificate.

If you don’t wish to install CSE or can’t (Web-based e-mail client or non-Windows OS) you can use Comodo WebReader to Read such e-mails.

I hope that this post will help you to resolve this issue.
Feel free to ask any questions on CSE.

Regards, Eugene.


Windows XP, SP2, Outlook 2007
On reciept of my email, followed instructions and downloaded/installed currently published vers of CSE

Windows XP, SP2, Outlook 2007
CSE - downloaded/installed currently published vers of CSE
To recreate the problem, send the same mail to myself

  • neither of us can read the email
  • as the originator, I must have the appropriate cert?
  • the .dat attachment, is not assigned to any app., that’s why outlook does not recognise it