I have a domain, let's call it foobar.com. All of the MX records for foobar.com point to Google's mail servers because I am using Google Apps for your domain to manage it. It's great because everyone gets all the advantages of GMail, but our e-mail addresses aren't @gmail.com.
I also have a server. Primarily, it's a web server, but it also serves other things. One of the things it serves is the web site for foobar.com and also sites for various virtual hosts such as shop.foobar.com and forum.foobar.com. The server is running Ubuntu 8.04, because I like using LTS releases in production.
The thing is, there are various applications running on the server that need the ability to send out emails. Various applications, like the cron jobs, send me e-mails in case of errors. Some of the web applications need to send e-mail to users when they forget their passwords, to confirm new registered users, etc. Lastly, it's nice to be able to send e-mail from the command line using the mail command, or mutt.
How can I setup the mail on the web server to go through the Google apps mail servers? I don't need the web server to receive mail, though that would be cool. I do need it to be able to send mail as any legitimate address @foobar.com. That way the forum application can send mails with email@example.com in the from field, and the ecommerce application will have firstname.lastname@example.org in the from field. Also, by sending the mail through the Google servers, we can avoid a lot of the problems with the e-mails being blocked by various spam filters on the web. Google's SMTP servers are trusted a lot more than mine would be.
I'm pretty good with administering Linux systems, but I am absolutely brain dead when it comes to e-mail. I need step by step directions from beginning to end on how to set this up. I need to know every thing to install, and every single change to the configuration files that is necessary. I have tried following various howtos and guides in the past, but none of them were quite right. Either they didn't work at all, or they offered a configuration that is not what I wanted.
Please help. Thanks.