Insert delay after 50 emails?

My server will only allow me to send 50 emails per two minutes. (I only want to send 70 per day, so not a large number). Is there a way to insert a delay of a few seconds between each email, or alternatively to insert a 2 minute delay after 50 emails? I currently send three batches of 21 emails each, and if I could add a delay between each batch – “recipients per email”, that could also solve the problem.

Thanks.