NOTE: This creates the user and gives it a home directory: ~vmail.

The virtual mailboxes will be placed in this directory.

Virtual mailboxes allow us to unlink the users of the email system from the users on the underlying operating system. This means that there can be mailboxes associated with users that do not have Linux accounts, and those users that do have Linux accounts can have multiple email accounts.

NOTE:

• myorigin defines the domain used for outgoing messages.
• mydestination gives the non-virtual domains for which mail will be accepted. mydestination should not contain any of your virtual mail domains.
  • $mydomain is not contained in mydestination. That is intentional. It will instead be placed in the list of virtual mail domains (described later).

Postfix will reject any mail that it receives that is not destined for a domain or machine that is not listed in mydestination (or in the virtual mail domains defined later) unless it comes from a machine on the local network. In this way, mail from the local network can be sent to anyone out onto the open internet and mail from anyone on the open internet can be delivered to a known user, but Postfix will not act as an open relay.

• mynetworks defines the local network. In this case the local network is confined to the server itself.
• mailbox_size_limit = 0 is used to disable limits on the size of the mail that can be received into a mailbox.
• home_mailbox define the name of the mailbox used for local users. In this case the mail will be placed in a hidden directory in the users home directory and it will take the form of a directory itself (the trailing slash indicates that the maildir format should be used).

NOTE: This requires than an aliases file /etc/aliases exists.

You should not have to create this file nor change it, but if you do change it, you will need to run the following before the changes will take effect:

postalias /etc/aliases

NOTE:

• virtual_mailbox_domains defines the virtual mail domains for which Postfix will accept mail.
• virtual_mailbox_maps defines where the actual virtual mailboxes are defined. An example of this file is:

  /etc/postfix/virtual_mailbox_maps

  peter@sharewiz.net      sharewiz.net/peter/mail/
  peter@abcd.net          abcd.com/peter/mail/
  admin@sharewiz.net      sharewiz.net/admin/mail/

  • Each line defines a virtual mailbox and consists of two items.
    • The first item is the email address of the virtual mailbox (should be lowercase).
    • The second item is the physical address on disk.
      • Each of the second entries ends with a slash. This indicates that the maildir format should be used rather than the mbox format (maildir places the mail into individual files inside the maildir whereas mbox is one giant file that contains the all of the mail messages).
      • The mail directory for peter@sharewiz.net would be /home/vmail/sharewiz.net/peter/mail/.
  • Whenever you modify this file you must run postmap in order to Postfix to be aware of the changes:

    postmap /etc/postfix/virtual_mailbox_maps

• virtual_uid_maps defines the user of the owner of the mail files.
• virtual_gid_maps defines the group of the owner of the mail files.
  • In this case 997 is the user and group number that correspond to the vmail user (found in /etc/passwd and /etc/group).
• virtual_minimum_uid must be equal to or smaller than the UID specified in virtual_uid_maps. It is associated with a sanity check that make more sense if you were using more sophisticated set ups.