So we just finished a migration to Office 365. We corrected an MX record a few days ago so external mail would start working again (seemed to cut off suddenly). Ever since then, from 3 different companies (all from Tucson, we're in Phoenix), all messages received from these 3 are showing up as being encrypted. We had someone send a message to my work account and my gmail account - the gmail email pulls up fine, the work account receives as being encrypted. The MX record essentially bypassed our internal exchange server and secure mail gateway. Every other mail receives fine into our work accounts. OWA (outlook.office365.com) gives a warning "The S/MIME message wasn't decrypted successfully. No certificate was found".
ANY idea what we need to do, add, secure, etc?
Shawn