I’m not sure how about you but I’m always having the problems with testing emails functionality in applications.
There are always stuff like user account confirmation or some newsletter notifications which would be good to test out in dev mode. Here is proposed solution which I posted not so far as symfony plugin:
http://trac.symfony-project.com/trac/wiki/sfEmailPlugin
All the emails are stored as the plain text files into /log/mail/ folder (by default). And you will be able to browse/view them via sfEmail module.
In order to use this plugin just use sfEmail as a class for sending emails instead of sfMail ( $mail = new sfEmail() ) and don’t forget to make sure that your plugin will be able to create a folder mail in log directory or create it by yourself with 777 permissions.
Also if you are using mailer.yml file in your config folder make sure deliverability is not turned off for dev mode. Since in this case you simple won’t get any email at all ( I had such problem 😉 ).