Very fast. SalesCatalysts Email Marketing can send over 1 million emails in an hour. However, sending too fast may have negative impact on inbox rate as large email service providers may see your emails as spams. Your content hosting provider (website) may not have enough capacity to handle the surge on website visits and content display, so as your customer service team on handling enquiries. In general, you are allowed to send as fast as 10,000 emails / hour. Talk to our consultant if you need to send faster.