Sorry that doesn't work with GMail. All I can tell you is that it works fine with Mail, and probably would with most other standalone mail clients.

But it's not "my" software; I don't work for Now, I'm just a fellow user. If NUDC 5.x doesn't work for you, no one else here has a suggestion, and you can't or don't want to wait for Nighthawk, then another solution would indeed seem to be your only option. There are a number of applications specifically designed for mass emails; perhaps one of those would work better for you (though GMail seems to cause problems with a lot of apps, from what I've read).
Dave Sawyer
iMac 24 2.8GHz Mac OS X 10.6.2
PowerMac G5 2GHz DP Mac OS X 10.5.8
Windows XP, Vista and Windows 7