we are looking for a solution to enable automatically OME encryption on dedicated messages at-rest in users exchange online mailbox.
Background: We are migrating from Notes to Exchange (M365). The migrating tool does not have the option to migrate encrypted messages. So our idea was to temporarily decrypt the encrypted messages in Notes, modify the Header, then migrate and turn on OME encryption by a DLP policy for that messages when arrive in EXO. The problem is, that this works only with on the fly messages, meaning messages which are in transit but not with messages at-rest (pushed by EWS by the migrating tool).
Any ideas to solve this would be appreciated?
Regards