I have done a bit of digging to support what I'm saying. Hope this helps.
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Autumn (Marketo employee) wrote
here :
"Email suspended" is automatically set when email bounces to that lead with a bounce code that we believe is due to an antispam system. This blocks us from mailing the lead for 24 hours. (Check the email suspended at timestamp; 24 hours after this time, the lead is available for emailing again.) Email suspended is not the same thing as marketing suspended. Email suspended is an automatic response to a spam block bounced message, while marketing suspended is a status that you set manually or through a campaign flow action."Marketing suspended" is not a status that Marketo will automatically change. If your leads are being set to marketing
suspended, they have been set that way through a campaign flow action. To find out, take one of your example leads in this state and click on their activity log. Find the point where the lead has a data value change for marketing suspended new value is true. It should tell you the campaign that made the change, and you can work with it from there. If you need further assistance, please contact support.-----------------------------
... and to answer Michelle T, if I'm not mistaken, to de-suspend "marketing suspended leads, you have to change data value from is suspended TRUE to is suspended FALSE...