Running an email server requires a certain level of awareness above just installing the default server technology to do so, with problems for clean relaying further amplified on AWS where batches of Elastic IPs can be annoyingly blacklisted before they've even been allocated. De-listing EIPs, tweaking Postfix HELO and matching hostnames against MX & A records can be time consuming, however for an easier ride, along with quality benefits for content and feedback, you could just piggy back the AWS SES service as your client-side SMTP relay.
SES is Amazons highly scalable bulk and transactional email service for businesses and developers. Like all AWS components it's a PAYG service with a cost effective structure ($0.10 per thousand emails) along with a granular feedback loop which includes notifications of bounce backs, failed and successful delivery attempts and spam complaints. Authorised domains/email accounts are limited to 5 emails per second and 10,000 sends per 24 hour period, although hitting such limitations from your desktop client is probably not something you will be concerned about.
As yet SES only facilitates US endpoints which does induce a degree of latency for non-US clients above their regular (localised) SMTP relay, and yes, this is a downside, however it's not completely insurmountable and probably certain (or definitely maybe) that multi region functionality will drop in when you least expect it.
Here's a grab of the SES metrics window from my own account, as you can see I'm not exactly setting the email world on fire, but it gives you an idea for the type and format of stats available, and as you can see my email sends are 100% clean.
As usual if you need any help with AWS SES, or any other aspects of AWS feel free to get in touch and we can hook up for a chat - http://cirronix.com/contact. We're UK based but your location is no problem and I find Skype is invaluable for globalised client relations (even if it is owned by Microsoft these days).