undeliverable.The Mail Transport Agent
Several MTAs are available for Ubuntu, each with its pros and cons.
Normally they are hidden under the skin of Ubuntu, silently moving mail
between servers all over the world, with little or no maintenance required.
Some MTAs are extremely powerful, able to cope with hundreds of thousands
of messages each day, whereas some are geared more toward smaller
installations. Other MTAs are perhaps not as powerful but are packed full of
features. In this section, we take a look at some of the most popular MTAs
available for Ubuntu.
Sendmail
Sendmail handles the overwhelming majority of emails transmitted over the
Internet today. It is extremely popular across the Linux/UNIX/BSD world and
is well supported. A commercial version is available that has a GUI interface
for ease of configuration.
As well as being popular, Sendmail is particularly powerful compared to
some of the other MTAs. However, it is not without downsides, and you will
find that other MTAs can handle more email per second in a larger
environment. The other issue with Sendmail is that it can be extremely
complicated to set it up exactly as you want it. A few books are available
specifically for Sendmail; the most popular one has more than 1,000 pages,
which gives you an idea of the complex nature of the Sendmail configuration.
We can be thankful, however, that the default configuration for Sendmail
works fine for most basic installations out of the box, making further
configurations unnecessary. Even if you want to use it as a basic email server,
you only need to do some minor tweaks. The level of complexity associated
with Sendmail often leads to system administrators replacing it with one of
the other alternatives that is easier to configure.
Postfix
Postfix has its origins as the IBM Secure Mailer but was released to the
community by IBM. Compared to Sendmail, it is much easier to administer
and has a number of speed advantages. Postfix offers a pain-free replacement
for Sendmail, and you can replace Sendmail with Postfix without the system
breaking a sweat. In fact, the applications that rely on Sendmail automatically