Hey Nathan,
Thanks for reaching out to the community.
For this instance, I would recommend using Hobocopy. If you're using FreeNAS just create an NFS pool. Then using this documentation.
Or alternatively, you could use.
Backup your SmarterMail files to the NFS network drive.
Please let me know if this helps.
Kind Regards,
Zach Sylvester
System/Network Administrator
SmarterTools Inc.
(877) 357-6278
www.smartertools.com