There is always a chance catch-all or unknown emails will still bounce, and there is nothing we can do about that.
Catch-all emails are designed to receive any email sent to a particular domain, regardless of whether the email address actually exists. This means that if an email is sent to a non-existent email address within the domain, the catch-all email will receive it. However, just like any other email address, a catch-all email address can bounce if there is a problem with the email delivery.
Below are some potential reasons for continued failed deliveries or bounce notifications:
Invalid email addresses: Some email addresses that slip through validation could still be invalid, or their domain may not exist anymore.
Domain Issues: Emails sent from a domain with a bad reputation or from a blacklisted IP address may be marked as spam or be filtered. This could cause emails to go undelivered.
Technical issues: There could be a technical issue on the receiver's end that is preventing the email from being delivered. This could relate to internal server settings, temporary server outages, a full mailbox, or problems with the recipient's email provider.
Email settings: The emails might be intentionally blocked by email service providers with specific spam filters or settings because of its content, attachments, or sender email address.
If you do not want to run the risk of the aforementioned, and only want to send to valid email addresses, you may remove the catch-all and/or unknown from your settings and send just to 'valid' email addresses. Sending to only valid email addresses will significantly reduce the number of bounced or failed deliveries you will encounter.