I recently received an email with an encrypted attachment. This was blocked by Zimbra and placed in quarantine. In previous versions, there was the possibility to send the email again, but since version 8.0.6 this no longer works.
In previous versions of Zimbra, you could run a command which made it possible to send the email again. However, this command does not work in version 8.0.6. I came across a forum post where someone explained how to open the quarantine account via webmail.
You can find the answer in this forumpost:
This post made it possible for me to read the email and to download the encrypted attachment.