Hi,

The error “550 5.7.1 Mailbox unavailable - Record does not exist or has been deleted” means your Helpdesk email address is no longer working or reachable. This usually happens if the email alias (like support@yourdomain.com) was deleted, renamed, or its forwarding rule was changed. To fix this, check in Odoo under Settings > Technical > Email > Aliases to make sure the Helpdesk alias still exists and is linked correctly. Also, check your email provider (like Gmail or Outlook) to see if the forwarding from support@yourdomain.com to Odoo is still set up. If it was working before and suddenly stopped, it’s likely something was changed on the email provider’s side. Fixing the alias or forwarding should get your Helpdesk emails working again.

Hope it helps