The number of Campaign emails sent is different.

The number of Campaign emails sent is different.

When sending an e-mail newsletter using Campaign, I used a segment to send the newsletter, but the number of recipients registered in the segment and the number sent in Campaign are different.

Segment: 8337 items
Campaign: 8278 items (arrived: 8270 + 8 undelivered)

8337-8278=59 items
This means that this Campaign email was not even delivered to 59 cases.
Why does this difference occur?
Please tell me how to resolve the issue.