In one of my Rails applications I'm sending emails through the Gmail SMTP server and everything just works, mails are not going to spam and so on ... But there's one thing that concerns me, the 500messages/day limit the SMTP has, currently I'm over 350/day. I didn't find any official Google page where they talk about the subject, just blog posts that seems to be reliable. Then my question is what do you suggest me in order to be able to send more than 500messages/day? I would love to keep using the Gmail SMTP.
Any help would be appreciated.
Don't use GMail for what it wasn't built for. It wasn't designed as a mass-email system, although Google definitely has the firepower to do this.
Instead, perhaps use something like SendGrid to send your emails. SendGrid is designed for this and is just as easy (actually, probably easier) to set up with than GMail.
You can consider using more than one gmail account to access the smtp server, however you may have problems with ip limits (couldn't find anything on their docs about it). Another option is performing dns mx lookups yourself and reproducing your own smtp server by directly delivering the messages to the user's emails - but that can increase the odds of you being tagged as a spammer as your ip is not whitelisted as sender.
I think the best way is to create another gmail account and trying to reroute your connection to use it when one of the accounts reaches the daily limit. A vpn connection can solve that for you.
来源：https://stackoverflow.com/questions/3929457/reaching-gmail-smtp-daily-limit