I think the databoard &billing has error , we didn't send so much emails every day from 20th Apr. but your data-board show we sent 4-5K each day. actually we only send 1.5-2K each day!
Quỳnh Min commented
Yes, I had the same situation when I didn't send mail but the next day the data report showed that we successfully sent more than 6k but it makes no sense that it failed more than 5k mails in there. This has happened in the last 2 months.