Adding an Additional Mail Host

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If you want IMail Server to receive mail for a second e-mail domain that has its own set of users, you need to set up a virtual host for the second domain. For example, if your mail server provides mail service for the e-mail domain, domain1.com, and you also want it to provide mail service for another e-mail domain, domain2.com, you need to create a virtual host for domain2.com.

There are two types of virtual hosts:

• Virtual hosts with IP Addresses
• Virtual hosts without IP addresses

Note: Whether you use a virtual host with IP address or a virtual host without IP address, you need to make the proper DNS entries for your mail domain(s). See "Setting Up DNS for Multiple Mail Hosts" and your DNS documentation for information on creating these entries.

Virtual Hosts with IP Addresses

This is usually the recommended way to set up virtual hosts, because all of the capabilities of regular IMail Server hosts are available to virtual hosts with IP addresses. The only limitations of virtual hosts with IP addresses are:

• Each virtual host requires its own unique IP address.
• In Windows NT/2000, this requires the extra step of adding an IP address in the Windows NT TCP/IP configuration in the Control Panel (Network applet - > Protocols -> TCP/IP Protocol -> Advanced button.)

Note: If you are using Windows NT 3.5.1 or later, you can add up to five IP addresses in the Network applet. If you need to add more than five addresses, refer to the documentation for Windows NT/2000.

Virtual Hosts Without IP Addresses

Virtual hosts without IP addresses are easier to set up than those with IP addresses. For more information, see "Configuring a Virtual Host". The IMail Server computer will assign a virtual IP address for the selected domain. You can then use an MX record in your DNS to point the virtual host to the primary host (which has a real IP address). There are, however, several limitations of virtual hosts without IP addresses:

• So that IMail Server can tell which virtual host the user is associated with, when the user logs on, they must enter the entire userid@hostname.com string for their user ID. Some mail clients will not be able to connect to the virtual host to read mail. This problem exists because some mail clients either have length restrictions for user IDs, or they clip the user ID at the @ sign.

  You can set up the virtual host to use a different character to separate the user ID from the hostname, but then you must tell users use this character in their logon user IDs (for example, userid#hostname.com). To change the character, see "Appendix G. Special Registry Values."

• The LDAP, Whois, and Finger servers do not work with virtual hosts without IP addresses.

Virtual hosts without IP addresses are recommended when you have a shortage of IP addresses, or when you want to forward all mail for a domain to a user at another domain. As an example of the latter:

• Your primary domain is called abracadabra.com
• You want all mail sent to merlin.com to be forwarded to info@abracadabra.com
• To accomplish this, set up a virtual host without an IP address for merlin.com and do not create any users for merlin.com
• Set up a nobody alias for merlin.com pointing to a user ID on abracadabra.com
• All mail to any user at merlin.com will be sent to the specified user at abracadabra.com

Configuring a Virtual Host

To configure a virtual host:

1. Select the "localhost" folder in the left panel.
2. Click the Add Host button.
3. The "Virtual Host Configuration" dialog box appears.
   

   The Local Addresses list box shows all IP addresses set up in the Windows NT/2000 TCP/IP properties as well as any virtual IP addresses assigned by the IMail Server.

4. Select the IP address for the virtual host (in the Local Addresses list box) or click the Add button to assign a new virtual IP address to use for the new mail domain.
5. In the Official Host Name text box, enter the name of the
   mail host.

   The name you enter here will be used to address mail to the users on the virtual host. For example, if you enter mail.domain2.com as the mail host name, any users you add to the virtual host will receive mail at user@mail.domain2.com.

6. In the Aliases text box, specify alternate host names for which you want the computer to accept mail. For example, if your mail host name is mail.domain2.com, you can set an alias of domain2.com so that IMail Server accepts mail addressed to fred@mail.domain2.com and also fred@domain2.com. Multiple aliases are separated by a space.
7. In the Top Directory Name text box, enter the name of the directory where the directories for users, lists, and web files for this virtual host will be stored.

   In most cases, you will want to use a different directory for each virtual host that you create. It is possible for virtual hosts to share a single directory but then users that have the same names will actually share the same mailbox.

8. Select the type of user database you want to use for this host.

   Use IMail User Database
   Use Local NT User Database
   Use External User Database

   For a description of these options, see "Chapter 2: Installation".

9. Enter the default parameters for mailboxes and messages. These parameters apply to all users on the virtual host.

   Default Max Mailbox Size. The default maximum size (in bytes) for the total of all mailboxes in a user mail account. If the total size exceeds the maximum, any new mail for the user is returned to the sender. Enter zero for an unlimited size.

   Default Max Messages. The default maximum number of messages (the total for all mailboxes created in the user mail account). If the maximum is exceeded, any new mail for the user is returned to the sender. Enter zero for an unlimited number.

   Single Message Max Size. The default maximum size (in bytes) for a single message sent to the server. If a message exceeds the maximum, it is returned to the sender. Enter zero for an unlimited size.

   Maximum User Count. The maximum number of users that can be registered for the domain. Enter zero for an unlimited number of users.

Note: Note that this does not apply to virtual domains that are based on the Windows NT user database or an external database. Furthermore, the displayed counts of users for domains that use the NT user database or an external database may not be correct.

Click Save to save the new virtual host configuration. Click Exit to close the "Virtual Host Configuration" dialog box.

10. After you've created the virtual host, you need to add user mail accounts. For information on creating and modifying user mail accounts, see "Working with User Mail Accounts"..

Setting Up DNS for Multiple Mail Hosts

For background information about DNS setup, see "Appendix J: Mail Servers and the DNS".

For a virtual host with an IP address, you need to make the following entries in your DNS:

• An MX record for the mail domain (for example, mail.domain2.com). The MX record identifies the host name of the virtual host.
• An A record for the host name of the virtual host. The A record maps a host name to an IP address.
• A PTR record for the IP address of the virtual host. The PTR record maps an IP address to the host name and is used for reverse lookups.

As an example, the DNS entries for a virtual host for which the host name in IMail Server is mail.domain2.com would look like:

SOA 
$ORIGIN 
... 
domain2.com 
     IN MX 10 mail.domain2.com   (MX record) 
     mail IN A 156.21.50.10      (A record)  
	(PTR record 
5.50.21.156.in-addr.arpa.,type = PTR 
 host = mail.domain.com 

A DNS lookup for mail sent to user@domain2.com would find that the mail must be sent to the host mail.domain2.com.

For a virtual host without an IP address, you need to make only one entry in your DNS: an MX record for the mail domain (for example, mail.domain3.com). This MX record identifies the host name of the primary mail host. As an example, the DNS entries for a virtual host without IP address for which the host name is mail.domain3.com would look like:

SOA 
$ORIGIN 
... 
domain3.com 
     IN MX 10 mail.domain.com  

A DNS lookup for mail sent to user@domain3.com would find that the mail needs to be sent to the host mail.domain.com.

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