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Google Workspace enforces a limit on the number of messages a user can send in a day, including the number of recipients per message. This is done to ensure that compromised accounts are not used as a vector to spread spam or malware, in addition to protecting the institution from malicious actors.
Exceeding this limit may cause your Gmail account to become temporarily rate limited or suspended. Our Google Administrators are proactively monitoring for alerts of user-suspension due to excessive messages, and will reach out to affected users to verify activity and take appropriate actions where necessary. This may include an inquiry about activity, a request to reset the user's password, and assistance with alternate avenues for mass email communication if the activities were determined to be legitimate.
For more information on Google Workspace's limits on Gmail messages, please refer to their article here:
https://support.google.com/a/answer/166852?hl=en