I’ve updated Cedric Duval’s trash-folder patch to work with the latest development release of Mutt at the time of this writing (1.5.16). View the patch here: trash-1.5.16.patch

Apply it to your source tree like so:

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wget http://scie.nti.st/dist/trash-1.5.16.patch
patch -p1 < trash-1.5.16.patch

Enjoy!