in reply to Re^2: Simple problem with @ in string.
in thread Simple problem with @ in string.

Would my system command being called with "" instead of '' cause perl to do that to the string?

No; that would require Perl 5 to interpolate variables and then interpolate the interpolated values.

I suspect instead that the error comes from blat.exe or at least system. If you use the list form of system(), you may have better results:

system( '/blat/blat.exe', 'message.txt', '-t', $emailaddress );

This avoids any shell interpolation.