Hey sorry - just saw this, thanks for the help Daniel.
I ended up using WP-SMTP-Mail. It works great, but I wouldn't recommend using gmail or google apps email.
First, make sure the sender information matches exactly what is in gmail (if you're using that). Gmail will not send the email if it looks like it's a forged header.
I can't say it enough - I do not recommend using gmail for this. They have CAPTCHA issues, if the account sends more emails than they think it should be (some nebulous number that no one at google seems to know), they'll block it from sending until you visit the website and log in from a CAPTCHA screen. No notification, no nothing. It just stops... and usually takes us a couple of days to realize no one is getting the emails anymore. We send, at most, 20 a week to internal, same domain email addresses (post update information). Nearly every week, gmail disables the account.
Then, once every couple of months, they go a step further and suspend the account (for the same reason). You have to email them to ask for it to be unsuspended. In their response, they say it shouldn't happen again, but then, two months later, suspended.
There's supposedly a CAPTCHA unlock at http://google.com/a/domain.com/captchaunlock (or something) that removes those security precautions, but we filled out the form every week... and every week, it continued to happen.
We moved to AWS and use email relay and its worked perfectly for three months, without issue.