If you get a good build of calibre for macOS 10.12, please let us know as I am stuck at macOS 10.13.6 so that Sigil can support the most users, and would love to have a version of calibre 4.x to play around with.
If you run into build issues, just let me know and I should be able to help. macOS is my primary dev platform for Sigil.
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