Kerio MailServer can handle multiple independent email domains for which various parameters can be defined.

In Kerio MailServer, one domain is always set as primary (the one which was created first). When other domains are added, any of the domains can be set as primary. Users log into the primary domain with their usernames only, whereas they have to log into all other domains using their full email addresses. This is again best shown on an example:

The domain company.com has been set as the primary domain. A user is defined in both domains with the name user. The user will log into the domain company.com with the name user, whereas for the second domain the user will have to use user@anothercompany.com as a username.

Note: Users in the primary domain can also authenticate to the server using their complete email address.

This implies that unless a serious reason to set a particular domain as primary occurs, a domain which includes the highest number of users should be set as primary. That will make it simpler for as many users as possible to specify their usernames when connecting to the server.

User accounts are defines separately in each domain. Therefore, domains must be have been defined before accounts are created.