How to send out verification emails safely?

We are using Rails 3.0.X and running our web app on Heroku. We are using Google Apps Free edition which runs Gmail as our email service. Our app allows end-users to sign up via email. After which, we send the user an email verification to prove that he owns the email address he registered with.

Today, several users signed up at once, and instead of Gmail sending out the verification emails, it marked them as spam. As quoted from their开发者_Go百科 info page:

Here at Gmail, we work very hard to fight spam. This includes not only spam coming into Gmail but spam being sent out from Gmail as well. Believe it or not, spammers sign up for Gmail addresses in large numbers just to send out spam! To help do our part to keep this junk off of the internet, we bounce mail that we are confident is spam. Unfortunately, we aren't perfect and will occasionally bounce legitimate mail. We apologize for the inconvenience.

There are a number of ways you can inadvertently confuse our automated spam filter, by sending suspicious-looking or spammy text, for example. By far the most common problem is sending mail cc/bcc'd to large numbers of recipients ("bulk mail") to send out newsletters, invitations, etc. Since spam is sent to many recipients, our spam filter is slightly more likely to confuse bulk mail with spam.

I sent them an email explaining our problem. And how this could hinder our business if our verification emails are not sent out. I have yet to hear from them.

In the meantime, is it wrong that I am using Gmails email server to send out emails? Should we use our own mail server rather than the gmail server? I notice that Heroku has an addon called Sendgrid. Should I be inclined to use this service for sending verification emails instead?

Generally i find that if you can do it with a heroku addon then you should do that. The free option for sendgrid allows 200 mails a day which is probably enough for you - if it isn't then you're doing well and can afford the upgrade :) In my experience money spent on heroku addons is well worth it compared to the cost of developer time in seeking an alternate solution.