The latest Cygwin mutt release (1.5.20-1) deviates a bit from standard mutt. After attempting for a bit to get standard mutt to compile and run stable on a Win7 64-bit Cygwin install, I gave up. There is a bad memory leak causing mutt to spiral out of control when calling mmap/mmap64.
It appears the Cygwin release fixes this. The only problem is the Cygwin release doesn’t have the sidebar patches. With a a bit of work I patched in the sidebar code to the Cygwin release, recompiled, and got it working.
The patch can be found here: patch-cygwin-mutt-1.5.20-1-sidebar.txt
Get the mutt source from Cygwin, change to the source directory, and then run the following:
autoconf -f -Wall
./configure --enable-imap --enable-smtp... (whatever you want here - run ./configure --help to get options)
patch -p1 < <patch-file>
./mutt (to test)
Hope that helps.