Google limits the number of email messages users can send per day and the number of recipients per message. If you exceed the Gmail sending limit, you may see errors like:
After reaching one of these limits, Gmail will not let you send new messages for up to 24 hours. The sending limits are automatically reset after the 24 hour period and you can resume sending mails from your Gmail account.
Email sending limits per day are applied over a rolling 24-hour period, not a set time of day.
If Gmail is returning your email messages with an error saying you've reached the limit for sending email, here are reasons why that happens and what you can do to avoid Gmail from returning your email messages.
You have reached the Gmail sending limit for the day. You are sending emails through IMAP or POP email clients (Apple Mail, Outlook), or you are sending emails from different aliases or you are using multiple add-ons for sending emails.
Gmail may limit your email sending capability temporarily if 10 or more recipients have hit the "Report Spam" button for your email messages. You should not send unsolicited emails to people who have never agreed to receive emails from your address.
Gmail can reject your emails if their algorithms classify your email message as spam. This happens when you have words in the message that are seen as spam, or if you have links pointing to unknown websites, or if you have a large number of recipients in the CC or BCC list or you may have attachment that are seen as suspicious.