Sending Encrypted Messages
To send an S/MIME encrypted message, the sender needs a copy of each recipient's certificate. UT's on-campus Exchange environment allowed users to retrieve certificates from the Global Address List. However, that certificate data does not synchronize to the Office 365 environment, so this functionality is not available after the Office 365 Migration.
The Office 365 Team is aware of this issue, and are researching a solution.
Users will have to receive a digitally-signed message from another individual before being able to send an encrypted message to them. Once a signed message is received, users must store that certificate in their Contacts by creating a local Contact entry for that individual. After this process is complete, encrypted email is possible.
Note: This does not affect the receiving of encrypted messages.