Mail Server

A mailbox is a single file that contains email for a particular user. Mail is delivered to the system where the user's mailbox resides: the local machine or a remote server. A mail server is any system that maintains user mailboxes in its /var/mail directory.

The mail server routes all mail from a client. When a client sends mail, the mail server puts it in a queue for delivery. After the mail is in the queue, a user can reboot or turn off the client without losing those mail messages. When the recipient gets mail from a client, the path in the "From " line of the message contains the name of the mail server. If the recipient responds, the response goes to the user's mailbox. Good candidates for mail servers are systems that provide a home directory for users or that are backed up regularly.

If the mail server is not the user's local system, users in configurations using NFS software can mount the /var/mail directory by using the /etc/vfstab file (if they have root access) or by using the automounter. If NFS support is not available, the users can log in to the server to read their mail.

If users on your network send other types of mail, such as PostScript^TM files, audio files, or files from desktop publishing systems, you need to allocate more space on the mail server for mailboxes.

One advantage to establishing a mail server for all mailboxes is that it makes backups easy. Having mail spread over many systems makes it hard to do backups. The disadvantage of storing many mailboxes on one server is that the server can be a single point of failure for many users, but the advantages of providing good backups usually make the risk worthwhile.