By deleting the email address you are deleting the primary key in the Marketo database, so generally I wouldn't recommend that. I agree that leads with invalid email addresses are generally not very useful, but not sure why you would blank out the email address.
We've already deleted records that don't have email addresses. Only difference is that they remain leads in SFDC, as our two databases are not entirely synced. We also created a trigger that would sync them back to Marketo if the email address is updated. It's just difficult to know when it's finally time to purge records we can't reach because of insufficient data.
@ Jessie: just note that if you delete records in Marketo but not in SFDC, they will flow back into Marketo whenever the record is updated in SFDC. Unless you set up criteria-based sharing rules in SFDC that hide those records from Marketo.
Yes, Jep. Forgot to also mention we have a recurring batch campaign that deletes leads with no email address. Curious - does this seem like overkill on our instance? It just seems with the size of our database, there's some serious lag in performance, which has prompted us to delete records without email addresses. Or atleast the few Marketo people I've spoken with have told me it's attributed to the size of our database.
So what's the downside to deleting Marketo's "Primary Key?" My reason for wanting to blank out the email address is so that:
These names do not show up on lead/contact reports for someone who is running an email target list and forgets to filter out "Email invalid is True"
Sales reps don't try to email those leads/contacts using MSI - not realizing the email address is invalid. There's no great indicator for bounce backs through MSI so I'd rather them not try to email those names in the first place.