Ask HN: Difficulties of a web app that sends out emails?

Hey all,

I'm looking at creating a web app similar to http://doodle.com/ that -

- Sends out an email to a customer - Customer replies or clicks link and chooses date from a selection of potential dates - Original sender sees the choosen date and it's added to the calendar

However, after doing a little investigation it seems like there could be massive issues with emails being caught by spam filters etc.

Has anyone worked on a startup or project that sends out lots of emails and is there anything you can do to get round this?

Thanks all.