A lot of different things that will cause emails to bounce, unrelated to whether the email address itself is good or poor, can cause emails to bounce. Here are a few instances:
Your IP is restricted.
Your content has been classified as spam.
You are going over a specific ISP's rate limitations.
Your email is not set up in accordance with RFC Standards.
Grey-listed domains are not being handled correctly by your email application.
You were blocked by the recipient.
The recipient blocked you.
Obviously, none of the aforementioned instances indicate that the email address is invalid. It simply means that additional aspects that contribute to bounces must be addressed. You must have access to your SMTP Logs and evaluate the SMTP Codes to determine what is causing the bounce.
If your high bounce rate is not a result of any of the aforementioned problems, please let us know. But in order to look into it, we need the SMTP Bounce you received. We will look into any cleaning-related difficulties if you send the emails and the SMTP Bounce notice to support firstname.lastname@example.org