Just a quick heads up for everyone.
Rails 2.3.14 is not completely Ruby 1.9.2 compatible.
Specifically the vendored version of TMail in ActionMailer calls String#is_binary_data?. This method was removed from Ruby in 1.9.2.
I realize that this probably won't be fixed as Rails 2.x is EOL, but I'm just putting it out there in case other people run into the problem. Personally I'd advocate a fix, Rails 2.3 promised Ruby 1.9 compatibility and this breaks that promise.
A simple workaround is to copy the definition of the method forward and add it to the String class in an initializer.
Here is it for reference (copied from apidock.com)
(self.count("^ -~", "^\r\n\").fdiv(self.size) > 0.3 || self.index("\x00")) unless empty?