I was using Google Apps for my outgoing emails and switched to SendGrid a few months ago. I usually send 500-600 emails a day but with Google Apps I was hearing a lot of complaints about never getting the email.
It's been a lot better with SendGrid and SendGrid also tracks bounces so you dont send more emails to invalid addresses, which hurts your reputation on mail servers.
I'm on the 10,000 emails/month plan and go over every month but the overage charges are very reasonable
I definitely recommend using one of these email service providers (ESPs) until you're sending enough emails to justify the time/cost of setting up your own email service.