Check out how to understand when your emails are sent, and if they were sent so close together that they might have errors.

You have a plan to send 2 emails in fairly close proximity to each other. The second email however is reliant on whether or not a contact has been sent the first email so you build a query with the following as part of the criteria for the contact source of the second email:

• Has Not Been Sent Email 1 within the last 1 day.

You schedule both emails with pre-processing and send the second email shortly after the first. However upon reviewing the reporting you note that the second email sent to more than you expected and upon downloading the sent metric for both, you note that some contacts have been sent both emails.

Resolution

The reason for this is because the second email was sent too close to the first email. Check out the example of two emails sent only couple minutes apart:

• Contact Source: Brand A email name: Mailing1 Scheduled: 04/05/19 04:00:00 AM Blocking Start: 04/05/19 03:00:02 AM Blocking End: 04/05/19 03:02:11 AM Send Start: 04/05/19 04:00:00 AM Send Complete: 04/05/19 04:00:09 AM
• Contact Source: Brand B email name: Mailing2 Scheduled: 04/05/19 05:00:00 AM Blocking Start: 04/05/19 04:00:01 AM Blocking End: 04/05/19 04:07:08 AM Send Start: 04/05/19 05:00:00 AM Send Complete: 04/05/19 05:00:37 AM

The important piece to look at is the 'Blocking' start and end time of the second email vs the Send start and end time of the 1st email:

• Brand A email name: Mailing1 Send Start: 04/05/19 04:00:00 AM Send Complete: 04/05/19 04:00:09 AM
• Brand B email name: Mailing2 Blocking Start: 04/05/19 04:00:01 AM Blocking End: 04/05/19 04:07:08 AM

Blocking in this instance relates to the time it takes to sort out the contacts in readiness to send. Because the blocking time of the second email is the same as the send time of the first email, many of the contacts had not yet been sent to as far as the blocking process was concerned. The flag that would mark a contact for being sent the email would have come shortly after they had already been lined up ready to send to.

If pre-processing was not enabled for the second send or if the schedule for the send was later with a corresponding later pre-processing, then the send would have been successful because it would not start to block until after the first send had completed.