What would cause an email to still be pending delivery?

You’ll have to tell/show us much more about your setup.

If you’re not using Wait steps (meaning the Send Email step hasn’t even fired for more than 24% of recipients) there’s no way for emails to still be pending — that is, queued within Marketo’s send infrastructure — for an entire week. Marketo only retries for 24 hours or 48 hours for selected domains (aol.com is a known example). There’s no type of transient error that leaves emails queued for longer than that without a bounce in the Activity Log.

Are you looking at an email performance report? Sometimes you need to hit the little refresh button on the bottom of the report to get the most up to date statistics for your sends. Not sure if this is the issue you are seeing, but it is my suspicion due to the information that Sanford provided.

@crystal_mac please return to your thread and check responses.