IMAP email server on TrueNAS/unRAID for archival use only: suggestions?

I know that mere mortals shouldn’t use an email server on their NAS, whether on a Synology DiskStation or on a DIY build. But there are nice tutorials online on how to use Synology’s mail server as an email message archive, to which you can offload your messages from your client machines, and which you can access via IMAP, but without any send functionality/connectivity.

Is there a solution like this for unRAID or TrueNAS Scale?