When looking at the bounce report for a campaign, you may see that some of the bounces you received are marked as "internal" bounces:
Internal bounces can happen for multiple reasons, such as timed out connections between servers, exceeded limits, etc. They are different from soft or hard bounces, which are treated differently by MailWizz.
Generally, since internal bounces report temporary problems, you can retry sending to the email addresses that are marked as internal bounces, but only after you fix the problems described in the message column of the bounce report.
It is important to note that MailWizz does not take any action against these type of bounces.
We consider them caused by the infrastructure you are using (bad smtp server reputation, bad/slow network, etc) and/or by the infrastructure used by the target recipient email address.
You should always inspect these bounces and take action to remedy the problem that caused the issue, where possible.