Dan,
I looked up this particular lead and it appears that they have soft bounced for the past 8 emails we have sent them...
The purpose of my questions was an attempt to explain why 2000 emails were bouncing each send as it was a clean list upon initial import. However, if we are not removing the bounced emails from the next send, could it possibly be the same 1000 emails emails bouncing?

Hi Ashley - the point we're trying to make though is that Marketo does not have any rules in place for how it handles multiple soft bounces. It's up to you to define those smart campaigns. For example, we have this trigger campaign that's always running in the background:


And then we always include this filter (Avanade Emailable = TRUE) as a standard filter for all email sends to ensure we don't continue to send emails to leads that continue to bounce beyond a specific threshold (which could harm your reputation/sender score).
Also, just because your list is clean, email servers can and will reject emails sent from Marketo - for a variety of reasons, including:
- your emails are being sent from an IP range that has been blacklisted on some servers
- you haven't configured SPF/DKIM properly
- some companies block ALL emails sent from Marketo (even with properly configured SPF/DKIM)
Hope this helps.