Copy the destination
Use the unique forwarding address shown for the QuickDesk mailbox. Configure forwarding at the existing provider; QuickDesk never needs the original mailbox password.
Avoid loops and duplicates
Do not forward the QuickDesk destination back into the source mailbox, and check that only one provider rule handles the same message. Duplicate rules can create duplicate tickets.
Confirm with a fresh message
Send from an outside account with a new subject, then wait for the ticket. If it does not arrive, inspect provider forwarding status and Mailbox troubleshooting.