I was having troubles with receiving my verification email, so I was told to register with a gmail address. So I did, and it worked.
But, my username is now used. And I don't think that was a particularly good solution.
I examined the header on the mail I got on my gmail account, and it looks like you are sending out your emails from a locally hosted mail server. I'm fairly certain you wouldn't have these problems if you used a third party smtp relay like SendGrid.
If you can't figure out how to prevent your emails from being caught in spam filters, look into using SendGrid or something. No need to re-invent the wheel.
