@mktouser, Marketo automatically marks people as Email Suspended (temporary email suspension from non-operational emails) and Email Invalid (permanent email suspension). These fields come OOTB along with other emailability fields: Unsubscribed, Marketing Suspended, and Blocklisted. However, Marketo doesn't update these fields unless it encounters an email rejection (bounced), so it can't validate an email for its legitimacy before you send it in the first place.
Below are some of useful links:
Hard and Soft Bounces in Email: https://experienceleague.adobe.com/docs/marketo/using/product-docs/email-marketing/deliverability/ha...
How Does Marketo Decide Whether a Person Receives Email or Not?: https://nation.marketo.com/t5/product-documents/how-does-marketo-decide-whether-a-person-receives-em...
Maintaining a Directory of Leads Bouncing Emails: https://nation.marketo.com/t5/knowledgebase/maintaining-a-directory-of-leads-bouncing-emails/ta-p/30...
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