In the case of newly imported recipients, Inxmail Professional does not yet know whether these recipients can be reached. Only after the first mailing has been sent will Inxmail receive the information (via a hard bounce) that some recipients can no longer be reached (e.g. because their inbox no longer exists).
Depending on the email marketing tool you have been using, hard bounces may not have been handled the same way. This way, hard bounces may have been contacted over and over again. This means that, for example, only 90% of recipients will receive your first Inxmail professional mailing, and the remaining 10% will be hard bounces (the exact number depends on the quality of your address database).
In future mailings created with Inxmail Professional, these hard bounces will no longer be contacted. Bouncing behavior will normalize and you'll have a delivery rate of almost 100% again. By the way, you can recognize hard bounces by the red dot in the recipient table.
Background: The strict handling of hard bounces in Inxmail Professional ensures the excellent reputation of our dispatch servers. In addition, as a customer you do save costs because you do not repeatedly contact recipients who are not reachable anyway.