7.9  A company with multiple sites

Information and Requirements

The company in our example uses the only domain called company.com. Supposing a company has its headquarters in New York and a branch office in London. Kerio MailServer is installed both at the headquarters and the branch office (two separate licenses). The headquarters' server uses DNS name mail.company.com. The branch office's server uses DNS name mail-ldn.company.com.

We want the email transferred among local users in the branch office to be delivered locally, while the email addressed to users in the headquarters is really sent to the headquarters. The same thing should be guaranteed for the communication in the other direction — messages sent from the headquarters to the branch office must be delivered to the branch office's server.

A company with multiple sites

Figure 7.9. A company with multiple sites


Note: To keep the example as simple as possible, suppose that users boss and secretary work in the headquarters and users technician and programmer work in the branch office. The following description is focused on these special requirements — it does not include detailed configuration of the SMTP server, remote administration, etc.

Implementation

Headquarters (configuration at the primary server mail.company.com)

  1. In the company's headquarters (at the primary server mail.company.com) in  Kerio MailServer, set the company.com domain as the local primary domain.

  2. In this domain, accounts of local users are defined (of those who work in the headquarters).

  3. If Kerio MailServer is behind the firewall, it is necessary to make port 25 available for the SMTP service.

  4. Create the ldn.company.com domain where no users and aliases will be defined. Set the Forwarding tab under Domains in a way that email for the ldn.company.com domain is forwarded to the mail-ldn.company.com server of the branch office (see figure 7.10  Forwarding settings).

    Forwarding settings

    Figure 7.10. Forwarding settings


  5. Next, set aliases for all users at the branch office (Domain Settings → Aliases), in this case for the users technician and programmer. These aliases provide that email for corresponding users is delivered to domain ldn.company.com.

    Alias settings

    Figure 7.11. Alias settings


Branch office (configuration at the server mail-ldn.company.com)

  1. Create a local primary domain company.com with the alias ldn.company.com.

  2. In the local primary domain, create accounts for all users in this branch office (for those who will have local mailboxes at the other site).

  3. Set that email addressed to the domain company.com is forwarded to the headquarters' server mail.company.com, while messages with the domain alias in the recipient's address are not forwarded. This option guarantees that messages where username or its alias is not specified correctly in the recipient's address are caught.

    Anti-Loop settings

    Figure 7.12. Anti-Loop settings


Notes:

  • Set a secondary DNS MX record for the filial's server. This will help you avoid problems in case of the headquarters' primary server's failure.

  • The wildcard alias should not be used in branch office's server's, otherwise the email for the headquarters will not be forwarded.

  • If users want to access their email remotely (e.g. using Kerio WebMail), they will always connect to the server where their local accounts are created (i.e. users in the headquarters will connect to mail.company.com and users in the branch office connect to the server mail-ldn.company.com).

  • The Free/Busy calendar will display only information regarding local users of the particular server.