If this is for a business with properly gathered leads from your customers, use your EC2 instance to handle something like Interspire's Email Marketer program which takes care of the list management, email campaigns, opens/bounce/links statistics and abuse alert/unsubscribe mechanisms. There are several programs like this that allow you to be your own Email Service Provider with the statistics gathering advantages that they provide.
Have the mailing list management running on EC2 and use Amazon SES as your SMTP server to send the email out. SES expects the mail to be metered out at a reasonable rate and watches for excessive bounces and abuse complaints. If you've followed the rules as to opt-in, previous business relationships and getting permission to send, this is no issue. You then need to log into your DNS services, create your TXT records for SPF, Domain Keys and DKIM signing records. The SES console aids you in doing this.
Usually, your Web Hosting Service provides DNS name servers, the Zone Management should be readily visible in your cPanel/Plesk interface. This is where all the goodies for MX records and the aforementioned go. Otherwise you'll be using Amazon Route53 or your Domain Registrar's DNS Zone Management. Check with whoever's got the NS records that point to your website as typically, that's the heart of your ecommerce operation.
If you're worried about inbound mail, among others, RackSpace has a pretty good mail box system with decent spam filtration and plenty of storage and has proved to be a good MX as well as has Google Apps. The limitations on GA inbox receive size didn't work too well for our Art Dept, so we moved.
I'm not related in any way to any aforementioned companies, just currently doing research to disentangle us from marketing vampirage and using Amazon AWS to leverage it.