Here is a tutorial on what you want, I think!

Postfix is an MTA so it should send (from localhost) emails out of the box...

Or perhaps I'm just getting slow! :)

@Rodrigo - Curious why you would setup postfix with msmtp? AFAIK postfix (a full MTA as Chris states) provides all the functionality of msmtp (which only does outgoing mail - ie SMTP) so not clear why you would use both? I've never used msmtp but it seems like a good lightweight alternative if you only want to send mail out, but with postfix as well it would seem redundant.

This is Turnkey remember!

You can send emails with a simple PHP script without any opther configuration.

Just remember that postfix is bound to localhost.

If you want to prevent being flagged as spam there a few hoops you need to jump through.

I use the Joomla and Wordpress appliances (Based on LAMP) and do nothing more than setup a newsletter plugin then send out emails from the appliance. One client has 6,000 subscribers and sends out on average once a week. Replies are not important but we put an address in the reply to field which is a gmail account and check it when we have to in case someone decides to give feedback. You can always ignore this step.

And although it looks pretty good, it's probably a bit in depth for what you'll need to do (includes instructions on installing postfix from source, etc) so there's only a small amount of it that you'd actually need to do to get postfix to relay emails through gmail's smtp. A quick google turned up heaps of results on how to configure postfix to relay through gmail and it looks pretty easy, just a case of minor modifications to the existing postfix config.

But like Chris says above, it's configured to send emails OOTB so unless you have some reason to relay through gmail, then it should just work as it is...

Maybe we should ask what you are trying to achieve like sending from php mailer or system notifications etc

You will find that postfix is fine but your ISP (Internet Service Provider) is flagging the email as spam for one or more of the following reasons.

1. Dynamic IP on appliance - even though the IP may be static in the respect it does not chsnge Amazon list it as dynamic and Trend Micro via their DUL list flag your server as a big bad spam producing machine.
2. DUL (Dialup Users List - bad acronym really) is a list of all the SOHO and once off servers that have not specifically proven they are ok to send emails.
3. Bad HELO name - this is the fully qualified domain name of the server. If its wrong (most would be if using TKL) then you will probably get flagged as SPAM
4. SPF (Sender Policy Framework) Records - at a zone manager level you need to specify this TXT record so emails have the status as "Pass" reducing the risk of being spoofed and giving recipients a nice warm feeling that you are a good guy.

I have listed out how to fix this issue in THIS thread and thought I had finished a wiki entry but just checked it and found it was half done! ARGH!

In addition to the info provided you can check your IP status with Trend HERE

Good luck and any questions, reply to the thread!

We all like to share...

If you divert all your mail through Gmail's SMTP you will have to play by their restrictions. I know one of them is no more than 100 emails an hour - useless for mailing lists.

You can configure your VPS to send emails as suggested above without much work and thats what I recomend.

As for certificates I generally dont bother as SPF and not being on a spam list work great but if you really want to certify emails there are tons of tutorials for getting it working from your VPS.