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 be difficult. The mbox files are especially prone to
problems if the files are being accessed over a network and can result in
file corruption; you should avoid accessing mbox mail mounted over
Network File System (NFS) 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 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 it is the best one for your
circumstances.Choosing an MTA
Other MTAs are available for use with Ubuntu, but those discussed in the
previous sections are the most popular. Which one should you choose? It
depends on what you need to do. Postfix’s main strengths are that it scales
well and can handle large volumes of email at high speeds, not to mention
that it is much easier to configure than the more cryptic Sendmail. However,
you may find that there are specific things you need that only Sendmail can
provide. It is easy to switch between MTAs when you need to.