If your domain is company.dom, then:
Create an MX (mail exchange) record for company.dom pointing to "email-guru.com." or "email-guru.eu."
Create a CNAME (alias) record for the subdomain mail.company.dom pointing to "email-guru.com." or "email-guru.eu."
Point your browser to https://email-guru.com:9010/Admin/company.com to access the secure WebAdmin Interface.
Use the Domain Administrator account name and password you received when your company.dom Domain was created.
They should specify email-guru.com (or email-guru.eu) as the "Server Address". If a port number can be specified for SMTP settings, they should use the port 587 instead of the port 25.
They should set their "User name" settings to accountName%company.dom, where domain.dom is your domain. Essentially they should use their Email addresses, but with the '%' symbol instead of the '@' symbol.
They should point their browsers to https://email-guru.com (or https://email-guru.eu), and enter their "User names" as accountName@yourdomain.dom or accountName%yourdomain.dom, i.e. they should use their Email addresses there.