Error FYI-2120 "Unable to add guest user, this email appears to be associated with an existing user."

Issue

When trying to share documents with a client or contact using New Collaborate, the following error is displayed:

• This email appears to be associated with the user (email address). Enter a new email address or update the associated email addresses for this user.

Cause

When adding a client to SharePoint, Microsoft identifies guest user emails associated with both existing internal and guest user accounts. Microsoft does not allow new guest user accounts to be created where the email address has already been associated with an existing guest user as an Other Address or a Proxy Address.

The error occurs when the guest user is linked to an existing account.

For some email domains, Microsoft uses the MX records of the primary domain, and redirects the email. For example, the MX record for icloud.com captures emails sent to icloud.com.au, and redirects it to icloud.com. Using hotmail.com.au returns the same error message, whereas Gmail allows both .com and .com.au domains.

This means that in some instances, you will encounter the error message even where there is no Other Address or Proxy Address present.

Solution

Depending on where the email association is located, you may be able to remove the association from the user's account on the Microsoft Entra Admin Centre.

Step 1 - Check if there is an Other or Proxy Address Present

Review the User Email Addresses

1. Log into the Microsoft Entra Admin Centre
   
   
2. From the menu on the left click Users - All users.
   
   
3. Locate the email address listed as the "associated with" email (the second email in the error message).
   
   
4. Click on the Display Name to open the user properties.
   
   
5. From the menu at the top, click Properties.
   
6. From the Contact Information section on the right, click the Other Emails field View link.
   
7. A list of emails will be displayed. Close the window after reviewing the list.
   
   
8. Repeat the steps by clicking on the Proxy addresses field View link.
   
   
9. A list of emails will be displayed. Close the window after reviewing the list.

If the Email is listed as an Other Email List

If the email address you're attempting to share documents with is listed in the Other Email list, you will be able to remove it from the contact information.

1. Click the Edit pencil icon at the top of Contact Information.
   
   
2. Click + Add email to display the Edit Other emails drawer.
   
   
3. Click the Trash can icon to delete the conflicting email from the list.
   
   
4. Retry sharing documents with the user via New Collaborate.

If the Email is listed as a Proxy Email Address

Proxy email addresses cannot be managed in Microsoft 365. 

If the client wishes to use the proxy email address:

1. The user will need to be deleted from the Sharing Settings for any other clients they may have access to. Refer to Removing Access to the New Collaborate Shared Folders
   
   
2. The preferred email to be used should then be added to the required Sharing Settings. Refer to Sharing the Share Folder and Upload Folder with Clients

If the guest user wishes to continue to use separate email addresses to access the New Collaborate SharePoint site, they will need to speak to their IT Administrator. Their primary email account will need to be updated to change the proxy address details. Refer to the Microsoft article Manage user mailboxes in Exchange Online

Step 2 - If there is no Other or Proxy Address

You will need to delete the guest user from the client's Sharing Settings in FYI before re-adding the email address using the correct address. 

Refer to Removing Access to the New Collaborate Shared Folders