At Robly, we stage (or throttle) email campaigns. If we didn’t do this, ISP’s would get very mad at us and block all our IP’s.
To protect ourselves from SPAMMERS who could ruin the reputation of our IP’s for everyone else, if we’ve never sent to email addresses on a list before, we break the list up in to small batches, send a batch, wait to see what comes back, and send out more if you didn’t trip our bounce or SPAM thresholds.
Your first campaign may take up to several hours to send. Once we’ve sent to an email address and we know it’s a good address, we batch emails in much larger, faster batches. Your subsequent sends will go out much quicker.