All mail servers were not created equal. Some give GroupMail users free reign to push messages through. Others have limitations on how many messages can be processed at any time. To counter this disparity, GroupMail developers made it possible to stagger the delivery of a campaign so that it can meet various mail server requirements. You can increase or decrease delivery connections and batch your delivery in segments in line with your own mail server capacity.

For more information and a screenshot of the Delivery Options console where these changes can be made, read Managing Email Delivery with GroupMail.