I tried to find that in google, here is what I have so far:
That's because Google places all sorts of limits on the use of its SMTP service by marketers. Those limits begin with a restriction on the number of recipients who can receive the same message. If Gmail's SMTP server detects that your message is going to more than 500 people, it disables your account.
So Gmail should still work for new lists of less than 500 subscribers, or if you're segmenting your list into chunks of no more than 500 — or if you want to test a subject line or content by sending two different messages to fewer than 500 subscribers each to see which message delivers the best conversions.
Sadly, that's still no. Google also disables accounts which sends "a large number" of undeliverable messages. It doesn't define that number but every subscription list always picks up some garbage addresses that people have entered to see what happens or to download the bonus on offer without having to supply a real address. Even if you only have a list of 500 subscribers, you still run the risk that Google will send you away from your emails for a day if it decides that too many people didn't receive your message.
Not sure, if it's a real information...