Email Spreadsheets uses the Gmail API service to send emails and there’s a daily email sending limit applied by Google to every Google account.
The email sending limit varies based on the type of your Google account.
If your Google account is using the free Gmail service to send emails, your daily email sending limit is 100 recipients per 24 hours.
If you have a paid Google Workspace account, your Gmail sending limit is 1500 email recipients per day.
How is Email Quota calculated
When you send an email through Gmail, a recipient is any "To", "CC", or "BCC" address in the outgoing message. The daily sending quotas are based on the number of recipients, rather than on the number of email messages.
Thus if you send an email with 2 recipients in the To field and one recipient in the CC field, your daily sending quota will be reduced by 3 (To=2, Cc=2=1) recipients after sending the email.
If you have just upgraded to Google Workspace, your email quota may be limited during the trial period.