A user is receiving Vault email notifications on a mobile phone that references another Vault.
There is an invalid contact on the iPhone contact list.
Check the iPhone contact list to determine if the contact name references the vault and uses firstname.lastname@example.org as the email address. This may reference a different vault in the domain.
To resolve this issue, search through the iPhone contact list. If this contact is present, delete it from the iPhone.
Vault Help Documentation: Email & Messages Administration