Sending Programmatic Email Messages

I'm looking to send email messages programmatically from my websites. For example, if people register their email address, I would like to email them to confirm their email address. To do this I will need to use an email sending tool and plug into an smtp service. In the past (7 or so years ago) I used Jmail, however, I am not sure what are the best services to use today and how spam filters have envolved!

I have three specific questions:

1. Does it matter which service I use to send emails programmatically (e.g., PhpMail, Jmail, etc.)? If so, which tools would you recommend?

2. How should I host this tool? I plan on sending a large volume of emails (thousands to hundreds of thousands). Would it make 开发者_如何学运维sense to use google-app-engine mail service to do this, or should I just host it on my own server (e.g., have my own SMTP server)?

3. I don't want my emails to be sent to spam folders, how can I ensure that the emails are received by the users?

Thanks!

No, you don't need your own. Based on the tags of your message, I'm going to assume you are using java and deploying your app on Google App Engine?

http://code.google.com/appengine/docs/java/mail/