Create a table with three columns; contact id, date and count. This will store how many times an email has been sent to each contact and the date the mail was sent, so;
id, date, count
123, 1 Sep 2015, 3
means contact 123 has been sent 3 emails on 1st Sept. Before you send an email get the date and count for the current contact.
If no row exists for the current contact then create one with today's date and 1 as the count and send the email.
If the date is not today then update the record for that contact with today's date and 1 for the count and send the email
If the date is today then update the row to increate the count by 1, and if the count exceeds the limit then don't send the email, otherwise send it.