I've recently set up my own email server. I've read several tutorials on how to install and configure Postfix and IMAP. One thing that I noticed is that if you send email from a server without a good reputation, there's a high probability it will end up in the Spam/Junk folder or worse, not even get delivered. I decided to leverage SES as my SMTP server instead of letting my local installation of Postfix do all the work.
sudo apt-get install stunnel
Add these lines to /etc/stunnel/stunnel.conf and make sure it starts properly (you may have to edit /etc/default/stunnel so that it starts automatically on boot):
accept = 127.0.0.1:1125
client = yes
connect = email-smtp.us-east-1.amazonaws.com:465
Update Postfix /etc/postfix/main.cf. There may already be smtpd versions but you need to add the smtp version of the options as well.
relayhost = 127.0.0.1:1125
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = may
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
Create/Edit /etc/postfix/sasl_passwd file with the contents and replacing username/password from credentials.csv
Execute the command line:
sudo postmap hash:/etc/postfix/sasl_passwd
A hash file is created. You can remove the original /etc/postfix/sasl_passwd file.
sudo rm /etc/postfix/sasl_passwd
sudo /etc/init.d/postfix restart
You should also update your DNS TXT field with an SPF record to bypass Spam/Junk folders:
"v=spf1 a mx a:yourserver.yourdomain.com include:yourdomain.com include:amazonses.com ~all"
You should also set up DKIM to have your emails less likely to be identified as spam.