7.9 A company with multiple sites
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## 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.

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).

   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`.

   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.

   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.

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7.8 Deleting of domains | Contents | 7.10 Setting up the backup mail server