Hello Bente
A recipient will generally be blocked because of one of the following reasons:
- they received 4+ soft bounces in a 3 month period
- they received 1 hard bounce
- they received your email and manually marked it as spam
To determine why somebody has been blocked, you would need to look at their email events from previous emails, not for the email where you see the blocked excluded email. You should be able to see something like soft bounces, invalid recipient events, etc, and if you open those bounce email events that is where you will see the message field containing the message provided from the recipient's mail server indicating why the email bounced.