When creating a meeting invitation in Microsoft Outlook and encrypting it with S/MIME via PGP Universal Server, the receipient using Outlook sees the meeting invitation as a text message and not as the expected meeting invitation object that can be added to the Outlook calendar.
When only using Microsoft Outlook with X.509 certificates added to the Windows Certificate Store for email encryption, standard email can be encrypted and signed with S/MIME. However, meeting invitations are always sent in the clear as Microsoft Outlook does not support S/MIME encryption on meeting invitations.
PGP Universal Server will encrypt the meeting invitation as any other e-mail message with S/MIME and send it as a message with the encrypted contents in the attachment Message.p7m as specified in the RFC. Any S/MIME capable client with the correct X.509 certificate including the private key will automatically decrypt the message contents. However, since Microsoft Outlook does not support encrypted meeting invitation objects, it will not detect this object as a meeting invitation and show it as text instead.
The message header of a meeting invitation contains: Content-Type: text/calendar; method=REQUEST; charset="utf-8"
The message header of an encrypted mail (also for encrypted meeting invitations) contains: Content-Type: application/pkcs7-mime; smime-type=enveloped-data; name=Message.p7m Content-Disposition: attachment; filename=Message.p7m
There are 3 options to work around this limitation:
1. Prevent encryption of meeting invitations. Meeting invitation works as expected, but not encrypted which can be a security risk. To prevent encryption of meeting inivitations:
In a PGP Universal Server managed environment
Add a rule to the mail policy of PGP Universal Server to send these messages in the clear
In a standalone PGP Desktop
Add a new policy for the account in PGP Messaging to not encrypt the meeting invitations. One example would be to add a policy to Send in Clear any message header which contains