MailEnable Professional Guide
Import users
Administration > Post office configuration > Post office actions > Import users

This feature allows you to import users to a postoffice.  A comma delimited file that is formatted as emailaddress,password,quota,friendly name  must be used. Password, quota and friendly name is optional.  If not provided then default settings are used and domains will be created if necessary. 

If quota limits are not specified in the file, these can be set to a certain limit, or unlimited.

If password settings are not specified in the file, a random password may be generated or a set password can be created for all imported users.