Urgent Help Required Please - Alias Email Id already registered by user not belongs to your organization.

Urgent Help Required Please - Alias Email Id already registered by user not belongs to your organization.

Hi I had this message when trying to move my business emails from outlook to Zoho.

Alias Email Id already registered by user not belongs to your organization.

I've now deleted this email address alias from outlook however, I still get the same message. Please can someone advise urgently how to fix this or I won't be able to receive customer emails.

Thank you.

Shaun