This can not be done with NME/MfNE in one migration run
Workround
In order to try and achiev this the only way to do this would be to run two separate migrations and chose Encrypted emails in one and not the other.
In the migration run which has Encrypted emails, chose a separate destination. However this PST will also have unencrypted data. This [PST] will then need to be purged to only hold the type of data required in each PST.
