Michelle,
Definitely use Marketo to manage these automatically. See a few of my posts on this topic:
http://www.slideshare.net/jdavidhill/marketo-email-reputation-management
http://www.slideshare.net/jdavidhill/data-management-in-marketo
http://www.marketingrockstarguides.com/six-principles-data-cleanliness-1566/
- Invalid to Valid
- Hard Bounced Management
- Multiple soft bounce suspension
- invalid and suspended issues