MDIR Versus Mailbox

Qmail also introduced maildir, which is an alternative to the standard UNIX method of storing incoming mail. maildir is a more versatile system of handling incoming email, but it requires your email clients to be reconfigured, and it is not compatible with the traditional UNIX way of storing incoming mail. You will need to use mail programs that recognize the maildir format. (The modern programs do.)

The traditional mbox format keeps all mail assigned to a folder concatenated as a single file and maintains an index of individual emails. With maildir, each mail folder has three subfolders: /cur, /new, and /tmp. Each email is kept in a separate, unique file. If you are running a mail server for a large number of people, you should select a file system that can efficiently handle a large number of small files.

mbox does offer one major disadvantage. While you are accessing the monolithic mbox file that contains all your email, suppose that some type of corruption occurs, either to the file itself or to the index. Recovery from this problem can prove difficult. The mbox files are especially prone to problems if the files are being accessed over a network and can result in file corruption; one should avoid accessing mbox mail mounted over nfs, the Network File System, because file corruption can occur.

Depending on how you access your mail, maildir does permit the simultaneous access of maildir files by multiple applications; mbox does not.

The choice of a mail user agent (MUA), or email client, also affects your choice of mail directory format. For example, the pine program does not cache any directory information and must reread the mail directory any time it accesses it. If you are using pine, maildir is a poor choice. More-advanced email clients perform caching, so maildir might be a good choice, although the email client cache can get out of synchronization. It seems that no perfect choice exists.

Ubuntu provides you with mail alternatives that have both strong and weak points. Be aware of the differences among the alternatives and frequently reevaluate your selection to make certain that it is the best one for your circumstances.

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