Gmail has a number of sending limits in place to prevent abuse of our system, and to help fight spam. If you reach one of Gmail’s limits, you’ll be temporarily unable to send mail. This limit is generally removed within 24 hours.Causes include, but are not limited to:

• Sending a message to more than 500 recipients.You can send a single message to a maximum of 500 recipients through the web interface, or up to 100 recipients when using POP access. Their email addresses can be distributed among the To, Cc, and Bcc fields. If you communicate with the same group of people on a regular basis, you might be interested in Google Groups.
• Sending a large number of undeliverable messages.We suggest verifying your contacts’ email addresses. Make sure the email addresses you’re sending mail to are valid. It’s also important that everyone you are sending mail to is willing to receive it.