Dirsync error when there is a matching target guest account - Error: "The proxy address "SMTP:user@domain.com" is already being used by the proxy addresses or LegacyExchangeDN" (4321024)

Dirsync error when there is a matching target guest account - Error: "The proxy address "SMTP:user@domain.com" is already being used by the proxy addresses or LegacyExchangeDN"

Performing a directory sync between tenants.
Source users cant sync to target if a Guest Account already exists for that user.

Is there a solution via the Quest tool to this? We cant remove the Guest Accounts as they are needed for access but we need to display all Mail Users from source in Target as contacts (existing Guest Accounts are hidden).

Error Message below confirms the Proxy Address duplication is the issue:

Error executing PowerShell script.
New-MailContact -Name "" -ExternalEmailAddress "SMTP:" -Alias "" -DisplayName ""
The proxy address "SMTP:user@domain.com" is already being used by the proxy addresses or LegacyExchangeDN of "#EXT#". Please choose another proxy address.
NotSpecified: (:ADObjectId) [New-MailContact], ProxyAddressExistsException

Incorrect Workflow Matching criteria

It is possible to sync between the source user mailbox account and the target guest account, but the key is the workflow matching criteria.
According to the sync log it cannot find the existing target guest account

Unable to match source object in to objects in : No matching object found.

It's possible the workflow Matching criteria is not configured to find the guest accounts, and this is causing the error in the write log

Review the following documentation regarding matching to an existing guest account, and make the changes needed to match the source object to the target guest account object: https://support.quest.com/technical-documents/binary-tree-power365/current/help-center/17#TOPIC-1564819