When trying to send 10 emails one after another (using PHP) I get an error

When trying to send 10 emails one after another (using PHP) I get an error

I am trying to send ~10 emails from php. It sends the first two emails but then after that I get "Swift_TransportException with message 'Connection could not be established with host smtp.zoho.com [ #0]'" . Could this be because there is a limit to how many emails you can send per minute or something like that?