The good news is that after 24 hours, google will lift the email restriction and you can send mail again.
The bad news is, theres no way to speed up or change that process, and if you send 500 messages at once or in the course of a given day, they would block you again for 24 hours.. This is from googles bulk sending guidelines for personal accounts.
You may see this message if you send an email to more than 500 recipients in a single email, or send more than 500 emails in a day.
When you get this error, you should be able to send mails again within 1 to 24 hours.
To prevent this from happening in the future, try creating a Google Group of all your email recipients and sending the message to that group's email address.
If creating a google group doesn't work for you, Id strongly suggest considering a service such as Mailchimps forever free plan.. If you are only mailing 500 people, you shouldn't go over the monthly limits to use Mail chimps mailing service for free.
As long as you dont send to over 2000 people at once, or send more then 12000 emails a month.. You can use mailchimp to send mail that appears to be coming from your same gmail account, and it wouldnt cost you anything extra, nor would it risk your gmail account being frozen and eventually blocked altogether.
If you have any questions or concerns, let me know!
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied.. I always answer follow up questions.
Senior Technician and Network Switching Systems Operator / Maintainer.