Its a bit of shame how our developer community handles password. I feel we should know better but unfortunately we are terrible at it. To send an email from your app you simply need to provide a few parameters (username, password) and you are golden. The only thing is that developers commit this sensitive information on github. I simply searched for the term "smtp.gmail.com" on github and bam loads of passwords! My observations,* I tried to login to some of the accounts and gmail asked me to verify who I was.
* Ruby community seems to be good about storing those details in the ENV
Case in point - NEVER DO THIS.
https://github.com/search?l=java&p=96&q=smtp.gmail.com&type=Code&utf8=%E2%9C%93