All non-anonymous leads which are in your Marketo database are counted toward your total database size. This includes unsubscribed leads and those with an empty email address field.
Yes, they count as one of your leads; one way to manage that is run a batch campaign that says something like If 'unsubscribed' and they don't have any activity for 6 mos, remove from database.
You can also export those leads before removing to keep for your files.
Also, Marketo has smart-unsubscribe, so if someone has unsubscribed, if they are re-added to the database, they're still listed as unsubscribed. Hopefully a Marketo person could elaborate on this for you, if necessary.
Delete lead will remove records from Marketo. Please note however, if you're not controlling the visibility of your sync user to these records, the next time they are updated in SFDC, they will be synched back down to Marketo as new.
@Jennifer there is step by step video in the university about how you can do this. The video is in the courses tab and called Admin SFDC 2 Hide recors from Marketo with the sync profile in SFDC.
If you have professional edition of SFDC support then the video won't apply to you, you'll need to reach out to support to discuss the options.
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