For 10 years, we’ve distributed Emailchemy for Mac as a .tgz file — a gzip’d tar file — but lately Mac OS X has been having trouble with it. So, now Emailchemy for Mac is a .dmg file download — a Mac disk image. If you have Safari setup to open files after download, the disk image will mount and open automatically. Otherwise, just double-click the .dmg file.
We’re not sure what changed in Mac OS X, but there have been a lot of reports of its built-in Archive Utility not unzipping downloaded zip files — and not just ours. We’re keeping the .tgz download on the site for now, so that we don’t break any links to our site, but the default download is the .dmg file.