Thanks - I see where you are coming from, but this is not directly what I aimed for with my initial post as a cheeky attempt to get consideration for a mail archiving app officially packaged for Cloudron.
nonetheless, I see both as valuable topic of discussion:
Legal compliance with business email archiving, especially in transactional email scenario - as a Cloudron feature tight to cloudron email server
Email archiving app, possibly providing the above functionality by delegation of the feature but also enabling the archive of other emailing solution not residing on Cloudron (e.g. gmail, outlook etc..).
Selfishly, the later is what is most attracting to me due to the need of archiving emails from various email solutions / providers as well as cloudron ones.