Methods for backing up gSuite (email) to local NAS

Goal

My goal is to backup the email (and maybe calendar/contacts) portion of my Google gSuite account. This is a personal email hosted on gSuite, so I can set permissions/configurations however necessary.

Requirements

  • Any software used must be open-source.
  • The destination of the backup is a SMB share on a TrueNAS server.
  • I must be able to browse the contents of this backup directory without relying on whatever software is used to create it. I.e. if the software used to create it ceases to be developed/function, I do not want to lose the ability to browse my backed-up files.

I’m aware of a solution that is specific to Synology devices (see this forum post from Tom ) however I do not have a Synology NAS and acquiring one for this sole purpose is not currently an option.

Does anyone have a software recommendation that would allow me to backup gSuite email to my NAS? Thanks!