Hi all,
For security reasons we want to add digital signature to all outgoing emails of the organization. I have problems with digital signed emails sent to external clients that not support the encryption format used by Outlook (S/MIME) as Gmail client, Yahoo client, etc. From some users, the emails sent to Gmail/Yahoo clients are encapsulated in a .p7m file and the body and attachments of the email can’t be read (only can be read using tools as p7mviewer). From other users, only the digital sign certificate is encapsulated in a .p7s file that appears attached to the email, but the rest of the email (body and attachments) can be read. In both cases the digital sign is not validated because certificates are signed by the internal CA, but the problem seems to be an Exchange policy/configuration that are applying to some user accounts, because in the emails encapsulated in the p7m format, the exchange server appends a banner (As you are aware, messages sent by e-mail can be manipulated by third parties. For this reason our e-mail messages …) and in the emails sent with the .p7s file attached the banner is not included in the email. Any of you know which may be the Exchange configuration/policy could be causing this behavior?
Thank you and best regards,
Victor