since today, QuarkXPress is available in Apple's Mac App Store.

https://itunes.apple.com/app/quarkxpres ... ls=1&mt=12
The variant is called "QuarkXPress 2018 Pro" and is very similar to QuarkXPress 2018 (available from resellers, Quark's eStore and from Quark directly).
Differences are listed here: http://www.quark.com/Products/QuarkXPre ... rison.aspx
There's also an FAQ available: http://content.quark.com/MAS-FAQ-EN.html
Price is $399 (and Apple's equivalents in other countries).
Until Nov 18 there's an introductory offer for $299.
Regards
Matthias
P.S.: Experiencing any issue? Send us an email to support@quark.com please.