Thank you for your reply. We have built our client list gradually over the past 12 years and I add new contacts to it gradually every week. We have now 35k contacts in our database and we normally send emails to about 25k of them. Every week, we send out 3 to 4 emails announcing our upcoming workshops on Sunday and reminders for the specific workshop coming up in two days. We have made no changes to the subject line or the date and time of the release. Up to April 4, we were doing well for ourselves at 11-15% open rate. Starting on April 6, the open rate dropped to 2% or less. At Constant Contact specialist's suggestions, I ran a A/B test on a different day but no improvement in the open rate. We will experiment with the Sender's name, subject line, day and time of day but given the day - April 6 - when the open rates dropped like a rock, we are asking the community if there were any technical changes made by Constant Contact that may explain this.
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