This metric tells you how many of your emails were accepted by the ISP. While it does not mean that the email reached the inbox, it does mean that it was not rejected or deferred by the ISP. Ensure that your email list is healthy; take precautions to prevent bad email addresses or spam traps from being added to your list.
A healthy email list, and one that will not incur sender reputation penalties, will have a limited number of bad or bounced addresses. If the email list that you are sending is your internally-collected house-list and you have a low deliverability rate, this may mean that you are not properly error checking email addresses at the time that people submit their email addresses, that you are not properly pruning and maintaining your email list, or that a malicious competitor has recently spammed your list by signing up a high volume of bad email addresses. In any case, if your deliverability rate is low (or the number of undelivered email addresses is high), your list requires immediate attention to restore it to full health. If your email list is a rented or purchased list and your deliverability rate is not acceptable, you should request a refund on a per-email address basis for the number of undeliverable addresses and should consider that factor when considering renting or purchasing email addresses from the same source in the future.
If you experience a low email Delivery Rate, take a look at where and when it happened. Determine if it’s isolated to one campaign or one ISP and make adjustments accordingly.
