First, let us mention that quota are imposed by Gmail. We have a dedicated page to explain how quota works, but in short all email addresses ending with @gmail.com or @googlemail.com have a limit of 500 emails/day. While Google Workspace accounts have a greater limit of 2000 emails/day.
When you use Mailmeteor, we are bound to these limits. To avoid sending errors, anytime that we detect that Gmail limits have been reached, we stop sending new emails and you will have to wait around 24 hours before sending new emails.
To avoid this situation, here are a few recommendations:
Prefer using a G Suite account over a Gmail address, this grants you much more quota.
Do not use multiple mail merge add-ons at the same time. The quota applies on your account, regardless of the tool you use to send emails.
Try to split your campaigns over a few days. This will increase as well your deliverability.