Batch email processing gives random results

We are trying to perform a batch print from a processed file.  There are 21 customers in the file and each requires that an email be sent, when we try and run through the process it seems to randomly email only a portion of the customers.  Last time it emailed 7 of the 21, for example.  

Also is there a way in sage to set the number of emails send per minute, or to set a delay between each email?