E-mail configurations for postfix/sendmail on AWS EC2 and SMTP services

StevenSmith asked:

I’m new to AWS. We are migrating Joomla websites hosted on a VPS at Hostgator to AWS EC2 running Red Hat. It needs mail services for sending and receiving.

I can install postfix and sendmail, but it isn’t clear how the SMTP works on AWS EC2 so that e-mail sent is connected is legit, and what exactly does it connect to? Does it need a 3rd-party service for SMTP mail or is this provided by AWS someplace?

My answer:

SMTP on EC2 works the same way as anywhere else, except that:

  1. Outgoing mail via SMTP port 25 is throttled; you can only send a very low volume of mail before messages are blocked. (You can apply to have this throttling removed, but unless 100% of your mail is transactional, don’t bother.)
  2. EC2 IP address ranges tend to go on and off various blackhole lists, meaning outgoing delivery likelihood is not very high, even if you are not throttled.

Incoming mail is not affected, except that you have remember to to open the appropriate ports (TCP 25, 110, 143, 465, 587, 993, 995) in your security group.

To resolve delivery issues, many EC2 users send mail through third party services such as Sendgrid, Mailchimp, Amazon SES, etc. You are not required to use Amazon to deliver outgoing mail.

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