Why is the sending of my email campaign delayed?

Why is the sending of my email campaign delayed?

The Tracking Statistics report allows you to view overall mailing performance, including sending performance and status. The column named Completed % indicates the percentage of completion, or delivery, for your email.

There may be times that the Completion % metric is less than 100%. Why is that?

There are a couple primary factors that can impact sending speed and completion:

  1. The speed at which recipient servers accept the sent email. Receiving servers can defer/delay or deny emails based on various factors such as load on the server and reputation of the sender. (most common) 
  2. The speed at which our software sends mail. Our mail servers send for hundreds of clients simultaneously. Though infrequent, at times there can be delays in sending due to volume within our system.
  3. At the time the campaign was scheduled, a send rate limiter was applied to slow the sending speed of the campaign.