Is it possible to use our admin account to globally access the mail archives for the individual e-mail addresses, or is it necessary to set up a separate account for each e-mail address?

It is not necessary to set up a separate account for each mail address. As a cluster administrator, you can log in to a domain via your customer account and access the entire mail archive. You can also set up an administrator account that can be used for logging in directly to the spam filter (https://login.europeanmx.eu). For more information about logging in and creating an administrator account, can be found in our FAQ article "How can I log in to the Admin-Panel (web interface of the filter)?".