My original post seems to have disappeared. I'm not at all sure how that happened.

For others who may need this information, here's how to configure CMSMailer to work with XAMPP and Gmail.

First, open php.ini and add or uncomment this line:
extension=php_openssl.dll

You should see a whole "extensions" section. Put it in that part of the php.ini file.

Then go into the CMSMailer extension and configure as follows:

Character Set: utf-8
Mailer Method: smtp
SMTP host name: smtp.gmail.com
Encryption: SSL
Port: 465
From address: your email address
From username: your name
Sendmail location: you can leave the default of /usr/sbin/sendmail
SMTP timeout: you can leave the default of 1000
SMTP Authentication: check the checkbox
Username: your Gmail address
Password: your Gmail password

Then "Submit" and then send the test email.

I hope this helps someone and saves someone some time. I don't know why my original post disappeared, but there you go.

Thanks jsh11a. I was having problems with CMSMailer and XAMPP and your solution worked perfectly.