My mass email limit has not exceeded then why am I unable to send more emails in bulk?

My mass email limit has not exceeded then why am I unable to send more emails in bulk?

You can send mass emails based on your  CRM Edition. The email count is calculated on a per-day basis, where 12 AM to 11.59 PM GMT is considered one day. The mass emails per day, per company includes Auto-responders, active email Schedulers, Macros and Mass emails.
You can also increase the mass email limit up to 2250 per day, per organization at an additional cost.  to increase your mass email limit. Also, check out the Campaigns Integration with CRM. You easily plan & execute campaigns and track the responses from contacts in CRM to take better sales decisions.