2.2.159 [RFC5546] Section 6.2 Recommendations

V0326:

The specification states that for an application where the information is sensitive or critical and the network is subject to a high probability of attack, iTIP transactions SHOULD be encrypted. This may be accomplished using public key technology, specifically Security Multiparts for MIME [RFC1847] in the iTIP transport binding.

Microsoft Office Outlook 2007, Microsoft Outlook 2010, Microsoft Outlook 2013, Microsoft Outlook 2016, Microsoft Outlook 2019

Outlook exports iCalendar data in clear text. The user can, however, save a meeting as an .ics file and attach it to an SMIME email.

On import, Outlook can receive digitally signed or encrypted SMIME data, which can contain an .ics attachment.