I don't have a startup, but I use Gmail for domains on my personal page. I just use postfix and some really basic scripts. Also, you might find these posts help

I don't have a startup, but I use Gmail for domains on my personal page. I just use postfix and some really basic scripts. Also, you might find these posts helpful: http://news.ycombinator.com/item?id=63836 http://news.ycombinator.com/item?id=63836 http://news.ycombinator.com/item?id=92022 http://news.ycombinator.com/item?id=92022