It should be possible to assign additional e-mail accounts to devices/user e.g. using a new General Mobile Policies type or through the ActiveSync server configuration.
This is possible with ZENworks Mobile Management 3.2.
This comes very handy if a given user needs to handle a generic mailbox like firstname.lastname@example.org next to his personal email account.
With the current ZENworks 2017 MDM implementation it is even not possible to manually connect with a different user account through ActiveSync if the MDM server acts as ActiveSync proxy. A ZENworks Primary Server only allows the device registered user to connect on ActiveSync.