We are about to utilize an external email archiving service but we need to be able to forward all mail to this service with TLS and authentication. Can mail forwarding or "Legal Intercept" with an SMTP host that requires TLS and authentication? The wiki section on this topic does not seem to indicate these features are supported for forwarding mail.

Enable archive forwarding to a third-party archiving server

If the archive account is not maintained within ZCS, you do not need to set a password, COS or other attributes as no archive account is created in ZCS.
1.
Log on as zimbra.
2.
Type zmarchiveconfig enable <account@example.com> archive-address account-archive@offsiteserver.com archive-create false