Upgrade or wait for reset when you hit 80%, 95%, or 100% of the monthly email allowance.
You got You are approaching your monthly email limit, Only N emails left this month, or Email sending is blocked because the monthly quota was exceeded.
Campaigns and workflows park. New workflow triggers are not queued until sending is active again.
80% and 95% are warnings only. 100% blocks sending.
This is not the provider daily SES quota — that’s How to fix sending rate or daily quota.