The time's come for Marketo to stop rewriting mailto: links. It's settled science that tracking such links makes them unreliable (see my blog post http://blog.teknkl.com/stop-trying-to-track-mailto-links-if-you-want-them-to-work/) and you can't expect users to remember to always uncheck the "Track Link" checkbox or include the "mktNoTrack" class.
Ultimately, the fact that they're tracked is a bug that needs to be fixed. It may be sad to see a (non-working) feature officially go, but there are plenty of new Ideas to add in its place.
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