Where can I see the actual messages of the bounce backs I got?

If you wish to review the actual bounce messages, you can either:

1. Uncheck the Delete after processing option for your #V2 mailbox (Setup / System Settings / System / Incoming email), access your #V2 mailbox account (e.g., via webmail) once you get bounces, then review the messages there
2. Set a forwarder so that a copy of each message received by your #V2 mailbox will be sent to another mailbox (this way you’ll prevent duplicate processing and the mailbox from being full)

Note that if you will be choosing #1, we strongly recommend that you re-enable the Delete after processing option once you have the data you need, as keeping it disabled will result to duplicate/multiple processing of the emails received by your a#V2 mailbox.

If you need to review your bounces for a long or indefinite period of time, going for #2 is the best option.