I'm unable to set up a normal user's email due to duplicate email addresses. In one case, I altered the SMTP of the external contact so I could use the appropriate address for my standard user account. The user's primary address is their real email address. There is no forwarding allowed on this Exchange server, so I'd like to know the implications of duplicate SMTP email addresses from external contacts.
SMTP addresses need to be unique within your Exchange organization, which is why you can't have the same SMTP address on a contact as on a mailbox.
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