I'm considering moving from a dedicated server to a VPS solution for email hosting for multiple domains/clients. I've already set up some VPS instances with ServerPoint.com to do spam/virus scanning for me, and now I'm ready to move away from my dedicated machine. ServerPoint had 2 hours of downtime last weekend to do scheduled maintenance on one of their machines -- I need a provider with shorter outages than that.
The problem is that I need lots of disk space (150GB to start, grow to 200+GB) relative to my CPU and RAM requirements. All of the VPS providers I've looked at (Linode, Slicehost, A Small Orange, Rackspace) offer fixed plans without the ability to add disk space. If I'm reading my MRTG stats correctly, I'm sending about 10GB out per day (I need to calculate how much of that is off-site backups).
Should I be looking at Amazon EC2 with S3 for storage? Looks like monthly fees of $15 for 150GB storage, $45 for 300GB transfer, $20 to reserve a "Small" instance and $21.60 for actual usage might fit my needs, and allow for growth. What do I need to know before going down the EC2 path? Reliability? Possible data loss? Backups to S3?
Are there other options?
EDIT: Additional details: Linux (currently Fedora, planning to use CentOS) with qmail, vpopmail (virtual domains), QmailAdmin (web interface to vpopmail), SpamAssassin, ClamAV, dovecot (IMAP). About 200 domains hosted.