How to remove leads with invalid emails from database

Marketo doesn't necessarily invalidate hard bounces, so this is not a good comparison. Once Invalid, Marketo won't send out email to those records.

See: http://www.slideshare.net/jdavidhill/marketo-email-reputation-management

The easiest way to handle invalid emails is to run a smart list, like you have, and then review and delete records as appropriate. The above slides have more detail on how Marketo handles hard bounces and invalid emails. You can add some flows to manage these too:

1. Email Invalid Restorer - remove invalid flag if email address is changed
2. Invalidate or Suspend hard bounced leads who bounced at least twice in past 30 days.
3. Check that smart list once a month to remove obviously bad records.

I strongly urge you to be careful with auto deletion.
See http://www.marketingrockstarguides.com/how-to-fix-data-disaster-in-marketo-1710/

Keep in mind that Invalid emails doesn't mean that the lead is completely bad. The record may be from a customer too, so someone needs to follow up to verify the email address.

Do you use workspaces and leaad partations in your instance? You may be limited to what your login can see.

On Josh's #2, I date and make a note of the frequent bounces in a field that can also be seen in SFDC.  I then remove them from our Marketo database.  Our list specialist will review the bad emails on the SFDC side and exclude them from any future email promos.  If it's a paid customer, our sales associates will call to get a replacement email.