1)500 messages per day:
You can hit the send button for 500 times in a day. 500 times you can send mail from your g-mail account each time in a day.
2)500 unique recipients per message:
In your each message you can add 500 unique recipients not more. Your limit for each mail is 500 if you cross the limit Google can temporarily disable your account if you send a message to more than 500 recipients.
3)2000 total emails per day:
You can send total 2000 emails from your G-mail account in a day. For example, you could send one message to a group of 500 people four times. 4 times 500 emails so it would be 2000 in total so you can send 2000 emails in a day.
4)Use POP or IMAP:
You can only send a message to up to 100 people at a time if you use POP or IMAP. If you exceed the limit, your account may be disabled for a day with the error – “550 5.4.5 Daily sending quota exceeded.”
5)Authentic e-mails address:
Whenever you will send mails make sure your e-mails address are authentic and corrects neither Google will treat these e-mails as spam and will temporarily disable your account.
Google, as per their program policies, can permanently disable your G-mail account if you doesn’t access to you Gmail account for the period of nine months. G-mail has many paid services by these you can customize your G-mail account and get the best services.