Emails could be marked spam if the email server is in EC2
Its a known fact that all the cloud offerings are different from each other. Weather they are big or small players, everyone is innovating at break neck speed and there is no point in comparing feature by feature because such a comparison could be obsolete before it is useful. I have a personal bias towards Amazon's EC2 because I have spent most time on it, and it seems to be far ahead of rest of the herd. However, I don't find everything easier and nicer in Amazon. Some use cases can be very simple and EC2 would be an overkill or insufficient. One example is if I want to host a website in the cloud. Sure, I could go with a traditional web hosting company, but if my requirements needed me to look at IaaS providers then there are a couple of things to consider.
I found setting email servers in Amazon extremely challenging. Part of the reason could be the way they have reverse DNS set up. First a few basic concepts. 1. DNS / reverse DNS: Without getting into too much details, DNS is what let you have names for a website (www.mycompany.com). Without it, we would have to refer to websites with IP addresses (e.g. 184.108.40.206). By looking up DNS servers the URLs (domain names) are converted to an IP address and the site is found and loaded. This is all transparent to the end user. Similarly reverse DNS (rDNS) allows programs to find names, given an IP address. One of the uses of rDNS is for spam email prevention by SMTP servers (emails servers). The mail servers check if the email actually originated from the DNS name that it says it came from. 2. How DNS is configured in Amazon instances: Each Amazon instance has an internal and an external DNS name. Usually you would map your wesites name (www.mycompany.com) to the external DNS of the instance. This would get translated to the internal DNS name of the EC2 instance. CNAME is used to make the mapping between your domain name and Amazon instance. (Also the suggested way by Amazon) However, if an email server is hosted on the Amazon instance and you send an email from the server, the reverse DNS resolves to the external DNS provided by Amazon, and not to your mapped domain name (www.mycompany.com). Therefore the email receiving server will not be able to correctly resolve the DNS name raising the probability that your emails from Amazon server are marked as spam. There are other options to host web servers and email servers where service providers have optimized the setup for exactly this purpose. I have only looked at a few and Slicehost (now owned by Rackspace) seems to have a very good offering and a network setup. I just wish it were a little cheaper.