I am having similar difficulties. I was able to send a message to a single address via SMTP, entered manually, not with gmail but with smtp.googlemail.com (port 465), but cannot connect when I specifiy a field for the address. If I select native mail client and that client is Apple Mail, it the address field works (but not for Thunderbird).
All the parameters work somewhere, but there is no set of parameters that work simultaneously for SMTP.
Is there a particular SMTP protocol required (for google)? (I am entering all values between quotation marks, with the exception of the port).