making sure messages / notifications do not arrive in the spam inboxes of other users?

Hi there, I am using Google apps as my mail mx records and I have noticed that some of my message notifications (things like te reminder to users to login if they have not been online in a while or the notification to tell users they have a new message or something) are basically ending up in the spam/junk areas of peoples mail clients like hotmail, gmail and outlook and so on. Is there anyway to make sure my notifications arrive in their inbox and not there junk boxes?

My site is not even live yet, I have never been blacklisted and basically have only sent out a handful of notifications and im concerned none of them are really arriving where they should be?

Thanks for your time on this.