This is a very large problem that Amazon needs to spend some time addressing. I run a fairly large production site on EC2 (14 instances) and when we went into

This is a very large problem that Amazon needs to spend some time addressing. I run a fairly large production site on EC2 (14 instances) and when we went into production we quickly found out we were unable to send email from our servers to anyone... just about every email provider has blacklisted EC2's address space. I literally have to run an "off site" server from Amazon as a mail relay to work around this issue. Word of warning, EC2 is awesome, but this is an important lesson learned if you are moving to the cloud.