Most email opens happen soon after a campaign is sent: http://www.quora.com/On-average-how-soon-is-an-email-opened-by-the-recipient-after-it-is-sent
Most email opens happen soon after a campaign is sent: http://www.quora.com/On-average-how-soon-is-an-email-opened-by-the-recipient-after-it-is-sent