It's easier due to the shape of the data.
For a contact, the settings only link to the ContactCode for the customer (eg. STMT), where you could import an updated email address easily, with user-friendly key fields for that table.
For an additional email address, it is recorded directly in the AR_CustomerDocumentContacts table, with no user friendly key for future updates... meaning you'd have to do a query, find the rows you want, edit them, and import that data...

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Kevin Moyes
Technical Systems Analyst
Munjal White Consulting Co.
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Original Message:
Sent: 04-14-2022 14:06
From: Doug Higgs
Subject: VI Import of Paperless Office Additional Email Addresses
@David Overholt Additional email addresses are definitely stored in AR_CustomerDocumentContacts. @Kevin Moyes Why does creating a contact code and adding the email address to the contact code make it easier to update the address later? Do you mean update the email addresses the document is sent? Why would this be easier. @Alnoor Cassim or @David Speck II Is there a way to expose AR_CustomerDocumentContacts for a VI import?
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Doug Higgs
Midwest Commerce Solutions, Inc
(312) 315-0960
Chauffeur, Chef, and Personal Assistant to Sprinkles
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Original Message:
Sent: 04-14-2022 13:14
From: David Overholt
Subject: VI Import of Paperless Office Additional Email Addresses
I Think the file you want is AR_CustomerDocuments there is a field for Contact Code in that table.