Hi Cat, Grace is spot on about the spam traps once being real email addresses. Like us, you probably have alumni who forget to update their contact information. (I've seen Compuserve email addresses!) In addition those who opened and clicked the few emails you have sent out from Marketo, you may be able to rule out potential culprits if you have any records of recent alumni interaction (e.g. donations, event registrations and/or email replies using the email address that's in Marketo).
If you have the email reputation powerpack (add-on with Marketo), a trick we've used is to include first name in the subject line, as subject line is listed in the spam trap hits - if they have an unusual name, it's easier to pinpoint.
In the absence of these options, you could also try sending emails in small batches to help narrow down to the spam trap. Recipients of an email that didn't hit a spam trap could be eliminated as potential culprits...at least for now.
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