Related Slack discussion about deceased contacts who share an email with another contact.

Elliott points out that a nightly silverpop export (tools/silverpop_export/export.py) is helping this situation: we get a list of all email address from the email log table that have ever been in civi and then if anything that is not associated with an active donor, it's send to the depression list, thus we do not need to store the secondary email to add it to suppression, it will go there from this silverpop export job, so for the first situation, donor will get both of their email in supression list, cause we replaced their exist primary email to the exist secondary email, thus the old primary do not associate with any donor, it auto add to supression list