exchange calendar invitation broken to external exchange/office 365 servers
When we send exchange calendar invitations it is broken to other exchange/office 365 servers but it appears to be ok when sent to linux servers
below is an example of a broken calendar invite when it is received. The receiver cannot accept nor does it show up on their calendar, they only get a plain text email. It also appears if we accept an external invitation but the acceptance is broken going back to them, it shows as not accepted/no status. All other emails appear to be ok in terms of richtext/html and people receiving our attachments. We have Exchange 2010/2016. This issues has existed before 2016 was introduced. The outgoing email is smart hosted thru our Cisco ESA Appliance aka IronPort.