You might have experienced the Error 550 5.4.5 Daily user sending quota exceeded. Exceeding of daily quota means that you've reached the limit of the number of emails that can be sent from your account within a day.
To resolve this issue, you can try the following options. By taking these ways, you should be able to resolve the issue and start sending emails again.
Wait for 24 hours before sending any more emails.
This will give your account time to reset its daily sending limit.
Upgrade your email plan to increase your daily sending quota.
You can contact your email provider to see if this is an option.
Reduce the number of emails you are sending each day.
You can try sending emails in batches or spacing them out over time to stay within the daily limit.
Use an alternative email provider.
Use an email provider that offers a higher daily sending quota.