Send Mail doesn't work with certain mail clients. (e.g. Thunderbird). In my experience, it has also been incompatible with the Outlook in Office for Mac 2011.
Maybe it's been fixed in some email clients. It's difficult to keep up with it. Why not publish for FBA members a list of tested mail clients and update it from time to time as information is submitted by developers and FM engineers? This would at least enable developers to troubleshoot client reports of incompatibility and perhaps avoid them in the first place by informing clients about compatible email clients.