Can you archive encrypted emails?

We cannot archive encrypted emails, including emails using an encryption service. Because your archived data has to be readable and intelligible by an auditor, encrypted emails are incompatible with archiving because their sole purpose is to make their contents unintelligible to anyone or anything outside of the recipient of the email.

If you are sending any sensitive documents to clients via email, to stay compliant you can use a service that encrypts just the document, not the text of your email.