You may have email addresses in your contact list that you can no longer reach. This may be because these email addresses have been blocked, or the emails are being returned because they cannot be received. These are called bounced emails. It is purposeless to keep these mail addresses in your contact list, so tidy it up.

You can find all invalid mail addresses on the Contacts dashboard via Marketing - Contacts. If you select a contact from this list, you will find the reason the mailings do not arrive under Contact information.

You can now replace this mail address, or delete the contact via Delete contact at the bottom of the page.