Are you looking only for opensource solutions or you may consider cheap/commercial which do the job seamlessly?
The budget is open source ⌠but if it works great, is inexpensive and makes life much easier, then yes, commercial products will be considered. 
I know that restic is another great alternative, many preferences for this or that software are determined by how much you are used to work with it.
Not sure whatâs wrong with python, or cython; about encryption, borg actually encrypts per default (you have to opt-out explicitly with borg init --encryption=none); borg also conveniently compresses (using zstd too) & dedups very, very efficiently. Comparisons between the two have been considered in various places, even on the restic forum itself where some possible advantages of borg are analysed. Some borg functionalities have been discussed in previous threads here as well
Both are good and preference is eventually pretty personal. About âOOBâ readiness: wrappers are available for borg but hey this is hostballs hostedtalk after all 
so I suppose some people hanging around here isnât reluctant to get their hands⌠dirty
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I am using borg for backing up usersâ Maildir files. Roughly several tens of GB but many tens of thousands of files. Things I like about borg is that it is really fast at finding changes and de-dupe. For an incremental on this quantity, maybe around 10-20 seconds to scan, dedupe, compress/encrypt, and upload to backend.
The excerpt I showed in the above-mentioned previous thread was taken from a mail server as well 
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